Method for producing optical compensating film, optical compensating film, circularly polarizing plate, and liquid crystal display

ABSTRACT

Provided is a method for producing an optical compensating film, which comprises stretching a cellulose acetate film, the cellulose acetate film having a water content of 2.0 to 20.0% by weight, wherein the cellulose acetate for the film has an acetyl value of from 57.0% to 62.5%.

TECHNICAL FIELD

The present invention relates to a method for producing an opticalcompensating film (especially λ/4 plate) of cellulose acetate. Further,the invention relates to the optical compensating film produced in themethod, and to an image display comprising it (e.g., reflection orsemi-transmission liquid crystal display, organic electroluminescent(EL) device-having display).

BACKGROUND ART

A liquid crystal display generally comprises at least a liquid crystalcell, a polarizing plate and an optical compensating sheet (phaseretarder plate). Concretely, a transmission liquid crystal displaycomprises two polarizing plates disposed on both sides of a liquidcrystal cell therein, and one or two optical compensating sheetssandwiched between the liquid crystal cell and the polarizing plate. Areflection liquid crystal display comprises a reflector, a liquidcrystal cell, one optical compensating sheet and one polarizing platethat are arrayed in that order.

The liquid crystal cell in such displays generally comprises rodliquid-crystalline molecules, two substrates for sealing up them, and anelectrode layer for applying voltage to the rod liquid-crystallinemolecules. Various display modes of liquid crystal cells are proposed,depending on the difference in orientation of the rod liquid-crystallinemolecules in the cells. For example, TN (twisted nematic)-mode cells,IPS (in-plane switching)-mode cells, FLC (ferroelectric liquidcrystal)-mode cells, OCB (optically compensatory bend)-mode cells, STN(super twisted nematic)-mode cells and VA (vertically aligned)-modecells are for transmission displays; and HAN (hybrid alignednematic)-mode cells are for reflection displays.

The polarizing plate generally comprises a polarizing film and atransparent protective film, and the polarizing film is generallyprepared by dipping a polyvinyl alcohol film in an aqueous solution ofiodine or dichromatic dye followed by monoaxially stretching thethus-dipped film. Two transparent protective film are attached to bothsides of the polarizing film to construct the polarizing plate.

Optical compensating sheets are used in various liquid crystal displaysfor solving a problem of image discoloration and for enlarging the fieldof view.

Of those, λ/4 plates have many applications, for example, for opticalcompensating films for liquid crystal displays, and antireflection filmsfor organic EL displays, and they are now in practical use. However,many λ/4 plates heretofore used in the art attain λ/4 or λ/2 only in aspecific wavelength range.

JP-A 27118/1993 and 27119/1993 disclose an optical compensating filmfabricated by laminating a birefringent film of large retardation and abirefringent film of small retardation in such a manner that theiroptical axes cross each other at right angles. The compensating filmcould theoretically function as a λ/4 plate in the overall range ofvisible light, so far as the difference in retardation between thelaminated two films is λ/4 in the overall range of visible light. JP-A68816/1998 discloses an optical compensating film capable of attainingλ/4 in a broad wavelength range, which is fabricated by laminating apolymer film of λ/4 in a specific wavelength range and a polymer film ofλ/2 of the same material in the same wavelength range as that of theformer. JP-A 90521/1998 also discloses an optical compensating filmfabricated by laminating two polymer films and capable of attaining λ/4in a broad wavelength range. However, the optical compensating film ofthe type fabricated by laminating two films has various problems in thatit is thick and its cost is high. Therefore, an optical compensatingfilm of a single film that realizes λ/4 in a broad wavelength range isdesired.

In this connection, JP-A 2000-137116 and WO 00/65384 have a descriptionrelating to an optical compensating film of a single polymer film ofwhich the phase retarder reduces in a shorter wavelength range, and toits application to circularly polarizing plates and reflection liquidcrystal displays. As the parameter of controlling the view anglecharacteristic of the above-mentioned λ/4 plate, employed is a numericalvalue defined by (nx−nz)/(nx−ny) (this is hereinafter referred to as anNZ factor). nx, ny and nz indicate the refractive index along the slowaxis in plain (the maximum refractive index in plain) of the phaseretarder, the refractive index perpendicular to the slow axis in planeof the phase retarder, and the refractive index along the thicknessdirection, respectively. WO 00/65384 says that the preferred range ofthe NZ factor is 1≦NZ≦2.

Preferably, the NZ factor is controllable. This is because, in a liquidcrystal display for image formation, the birefringence (Δn) of theliquid crystal cell varies depending on the liquid crystal panel thereinand the angle-dependency of Δn also varies depending on the liquidcrystal panel. Therefore, if the NZ factor of the optical compensatingfilm in the display is controllable, the view angle characteristic ofthe display can be optimized, requiring no change of the retardationvalue Re of the film.

However, the NZ factor is defined by the refractive indices in threedirections of the film, and is therefore correlated with the draw ratioof the film. Concretely, when the draw ratio of the film in the machinedirection increases more and therefore the film is most likely inmonoaxial orientation, then the NZ factor of the film comes nearer to 1from a larger value. In case where a λ/4 plate is fabricated accordingto the width-unlimited monoaxial stretching method described in theExamples in WO 00/65384, the draw ratio of the film that realizes aretardation of λ/4 is determined by the elongation at break of the film,and therefore the NZ factor of the film shall be indiscriminatelydetermined.

DISCLOSURE OF THE INVENTION

One object of the present invention is to provide a method for producingan optical compensating film (especially, a λ/4 plate that attains aphase shift of λ/4 in a broad wavelength range), of which can control NZfactor without a retardation change in the film, and which has a goodview angle characteristic, and to provide such an optical compensatingfilm having the advantages as above.

Another object of the invention is to provide a polarizing plate thatcomprises the optical compensating film as above and has a good viewangle characteristic, and to provide an image display device(especially, a reflection or semi-transmission liquid crystal display,and an organic electroluminescent (EL) device-having display) thatcomprises the optical compensating film or the polarizing plate asabove.

According to the invention, there are provided a method for producing anoptical compensating film, an optical compensating film, a polarizingplate, and a liquid crystal display mentioned below, which attain theabove-mentioned objects of the invention.

1. A method for producing an optical compensating film, which comprisesstretching a cellulose acetate film, the cellulose acetate film having awater content of 2.0 to 20.0% by weight,

wherein the cellulose acetate for the film has an acetyl value of from57.0% to 62.5%.

2. The method for producing an optical compensating film as described inabove 1, wherein the optical compensating film has a retardation valuemeasured at a wavelength of 550 nm (Re550) of 20 nm to 2000 nm: 20nm≦Re550≦2000 nm.

3. The method for producing an optical compensating film as described inabove 1 or 2, wherein the optical compensating film has a distributionof the retardation value measured at a wavelength of 550 nm (Re550) of10% or less in both a width direction and a longitudinal direction ofthe film.

4. The method for producing an optical compensating film as described inany of above 1 to 3, wherein the optical compensating film has:

the retardation value measured at a wavelength of 450 nm (Re450) of 60to 135 nm; and

the retardation value measured at a wavelength of 590 nm (Re590) of 100to 170 nm, and the stretched film satisfies the condition:(Re590−Re450)≧2 nm.

5. The method for producing an optical compensating film as described inany of above 1 to 4, wherein the optical compensating film satisfies theconditions: 0.5<Re450/Re550<0.98; and 1.01<Re650/Re550<1.35, in whichRe450, Re550 and Re650 represent the retardation values measured at awavelength of 450 nm, 550 nm and 650 nm, respectively.

6. The method for producing an optical compensating film as described inany of above 1 to 5, wherein the cellulose acetate film is dipped inwater and/or exposed to water vapor to absorb water, before the stretch.

7. The method for producing an optical compensating film as described inany of above 1 to 6, wherein no water film is substantially formed onthe surface of the cellulose acetate film when the cellulose acetatefilm is stretched.

8. The method for producing an optical compensating film as described inany of above 1 to 7, wherein the water content of the cellulose acetatefilm just after having been stretched is 2.0 to 20.0% by weight.

9. The method for producing an optical compensating film as described inany of above 1 to 8, wherein, when L indicates the distance between thefixing members for fixing the cellulose acetate film when stretching andW indicates the width of the cellulose acetate film measured in thedirection perpendicular to the fixing member-to-fixing member direction,the aspect ratio: L/W satisfies the condition: 0.1≦L/W≦2.

10. The method for producing an optical compensating film as describedin any of above 1 to 9, which comprises a step of stretching thecellulose acetate film between at least two pairs of nip rolls by adifference in the rotation speed between the at least two pairs of niprolls.

11. The method for producing an optical compensating film as describedin above 10, wherein, when W′ (cm) indicates the width of the celluloseacetate film and L′ (cm) indicates the distance between the at least twopairs of nip rolls, the aspect ratio: L′/W′ satisfies the condition:0.5≦L′/W′≦2.

12. The method for producing an optical compensating film as describedin any of above 1 to 11, wherein the film is stretched in water.

13. The method for producing an optical compensating film as describedin any of above 1 to 11, wherein the film is stretched in air.

14. The method for producing an optical compensating film as describedin any of above 1 to 11, wherein the film is stretched in water vaporhaving a relative humidity of from 60% to 100%.

15. The method for producing an optical compensating film as describedin any of above 1 to 14, wherein the film is stretched at a temperatureof 50° C. to 150° C.

16. The method for producing an optical compensating film as describedin any of above 1 to 15, wherein the film is stretched with a draw ratioof from 1.1 times to 2.0 times.

17. The method for producing an optical compensating film as describedin any of above 1 to 16, wherein the stretching time is 1 second to 30seconds.

18. The method for producing an optical compensating film as describedin any of above 1 to 17, wherein the optical compensating film satisfiesthe condition: 1≦(nx−nz)/(nx−ny)≦3, in which nx indicates the refractiveindex along the slow axis in plain of the optical compensating film, nyindicates the refractive index perpendicular to the slow axis in planeof the optical compensating film, and nz indicates the refractive indexof the film in the direction of the thickness thereof.

19. The method for producing an optical compensating film as describedin any of above 1 to 18, wherein the optical compensating film has ahaze value of 0 to 2%.

20. The method for producing an optical compensating film as describedin any of above 1 to 19, wherein the cellulose acetate film contains anaromatic compound having at least two aromatic rings in an amount offrom 0.01 to 20 parts by weight, based on 100 parts by weight of thefilm.

21. An optical compensating film produced according to the method forproducing an optical compensating film as described in any of above 1 to20.

22. A polarizing plate, which is a laminate including:

the optical compensating film produced according to the method forproducing an optical compensating film as described in any of above 1 to20; and

at least one of a polarizing film and a polarizing plate.

23. An image display comprising at least one of:

the optical compensating film produced according to the method forproducing an optical compensating film as described in any of above 1 to20; and

the polarizing plate as described in above 22.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a stretching step in which the filmto be stretched is dipped in water to absorb water and then stretched inwater vapor.

FIG. 2 is a schematic view showing a stretching step in which the filmto be stretched is exposed to water vapor to absorb water and thenstretched in water vapor.

FIG. 3 is a schematic view showing a stretching step in which the filmto be stretched is dipped in water to absorb water and then stretched inwater.

FIG. 4 is a schematic view showing a stretching step in which the filmto be stretched is exposed to water vapor to absorb water and thenstretched in water.

FIG. 5 is a schematic view showing a stretching step in which the filmto be stretched is exposed to water vapor to absorb water and thenstretched in water vapor.

FIG. 6 is a schematic view showing a stretching step in which the filmto be stretched is exposed to water vapor to absorb water and thenstretched in water.

FIG. 7 is a schematic plan view showing an obliquely stretching devicethat is used in Example 6.

FIG. 8 is a graphic view showing the constitution of the reflectionliquid crystal display of the invention.

FIG. 9 is a cross-sectional view showing the constitution of the VA-modeliquid crystal display of Example 9.

BEST MODES OF CARRYING OUT THE INVENTION

We, the present inventors have found that, when a cellulose acetate filmhaving an acetyl value (a degree of acetylation) of from 57.0% to 62.5%is made to positively absorb water and then stretched, its NZ factor canbe controlled. On the basis of this finding, the inventors have attainedthe optical compensating film of the invention that has good opticalproperties. The invention is described in more detail hereinunder.

[Acetate Film]

For the cellulose acetate film of the invention, preferably used iscellulose acetate having a degree of acetylation of from 57.0% to 62.5%,more preferably from 58.0% to 62.0%.

The acetyl value (degree of acetylation) is meant to indicate the amountof acetic acid bonded to the cellulose unit by weight. The acetyl valuemay be measured and computed according to ASTM D-817-91 (test method ofcellulose acetate).

The viscosity-average degree of polymerization (DP) of the celluloseacetate is preferably at least 250, more preferably at least 290.

The cellulose acetate for use in the invention preferably has a narrowmolecular weight distribution of Mw/Mn (Mw is a weight-average molecularweight, and Mn is a number-average molecular weight) measured throughgel permeation chromatography. Concretely, the Mw/Mn value of thecellulose acetate is preferably from 1.0 to 1.7, more preferably from1.3 to 1.65, and most preferably from 1.4 to 1.6.

Also preferably, the cellulose acetate film for use herein has a lighttransmittance of at least 80%.

[Water Content and Water Absorption]

The cellulose acetate film has a water content of 1.8% by weight at roomtemperature. In general, the cellulose acetate film (original film) isheated up to around its glass transition point (Tg) so as to bestretchable, and then it is stretched. When the film is heated up toaround its glass transition point, for example, up to 130° C., its watercontent further reduces and it will be 0.4% by weight. The invention ischaracterized in that the cellulose acetate film (original film) in thatcondition is made to absorb water before it is stretched, and the filmto be stretched is made to have a water content of from 2.0% by weightto 20.0% by weight, but preferably from 2.5% by weight to 18.0% byweight, more preferably from 3.0% by weight to 16.0% by weight.

The water content of the film is the water fraction (% by weight)contained in the film. Concretely, it is indicated by the following:Water content (% by weight)=0.1×(W/F)wherein W represents the amount of water (μg) in the film samplemeasured, which is indicated by the moisture meter used for themeasurement; and F represents the amount of the film sample (mg)measured.

Having the controlled water content of from 2.0% by weight to 20.0% byweight, the cellulose acetate film to be stretched may have a loweredglass transition point (Tg). For example, its Tg may be lowered from130° C. (when its water content is 0.4% by weight) to 75° C. (when itswater content is 5.5% by weight). Accordingly, the film can be uniformlystretched at a temperature lower than the ordinary stretchingtemperature (130° C.) thereof.

Tg of the cellulose acetate film having a water content of 5.5% byweight is measured as follows: The film is dipped in water in a closedsilver pan (70 μl), and its Tg is measured with a varyingtemperature-dependent DSC (TA Instrument's DSC2910).

In the invention, the cellulose acetate film (original film) to bestretched is made to absorb water before it is stretched, whereby itswater content can be controlled to fall within the defined range asabove.

For making it absorb water, the cellulose acetate film to be stretchedis dipped in water (water bath method) or exposed to water vapor (watervapor method), or the two methods may be combined.

When the film is dipped in water, the water temperature preferably fallsbetween 60° C. and 100° C., more preferably between 70° C. and 100° C.,even more preferably between 75° C. and 100° C. Concretely, thecellulose acetate film to be processed is passed through a water tankfilled with water having a temperature that falls within the definedrange, while conveyed by rolls set in the water tank in which it takesfrom 0.1 to 20 minutes, preferably from 0.2 to 10 minutes, morepreferably from 0.5 to 5 minutes between the rolls. Thus passed throughthe water tank, the film absorbs water.

For exposure to water vapor, the film may be exposed to water vaporpreferably having a temperature of from 60° C. to 150° C., morepreferably from 70° C. to 140° C., even more preferably from 75° C. to130° C., and having a relative humidity of from 70% to 100%, morepreferably from 80% to 100%, even more preferably from 85% to 100%, fora period of from 0.1 to 20 minutes, more preferably from 0.2 to 10minutes, even more preferably from 0.5 to 5 minutes. Thus exposed towater vapor, the film absorbs water. For example, rolls are set in aroom filled with such water vapor, and the cellulose acetate film to beprocessed is conveyed by the rolls in the room to absorb water.

Water in which the film is dipped or water for water vapor to which thefilm is exposed may be any and every one that is substantially water.The one that is substantially water is meant to indicate a substance ofwhich the water content is substantially at least 60% by weight, and itmay contain any of organic solvents, plasticizers, surfactants andothers except water. The organic solvent that may be in water for use inthe invention is preferably a water-soluble organic solvent having from1 to 10 carbon atoms. Preferably, however, water accounts for at least90% by weight of the water mixture for use herein, more preferably atleast 95% by weight. Most preferably, water for use herein is purewater.

The water bath method and the water vapor method may be combined or maybe carried out separately. Especially preferably, the water vapor methodis employed singly.

Before the cellulose acetate film thus processed to absorb water isstretched, it is desirable that no water film is substantially formed onits surface. A water film is readily formed on the surface of thecellulose acetate film processed in the manner as above to absorb water,but if it is kept still remaining on the surface of the celluloseacetate film being stretched, the cellulose acetate film will slip onfilm-fixing members such as nip rolls while it is stretched betweenthem. If so, the film could not be stretched with a desired draw ratioand, in addition, it will be readily scratched.

The condition that “no water film is substantially formed on the surfaceof the cellulose acetate film being stretched” in the invention is meantas follows: Filter paper is pressed against the cellulose acetate filmto be stretched, and the area of the filter paper having absorbed waterfrom the film is measured. The area thus measured is at most 30% of theoverall area of the filter paper.

For removing the water film from the wetted cellulose acetate film, onepreferred method comprises applying a jet of air onto the surface of thewetted cellulose acetate film through an air knife after processing ofabsorbing water to thereby blow off water from the surface of the film.In this method, if the vapor to be jetted out of the air knife is dryair, the water inside the film will easily evaporate away. Therefore, itis desirable that air having a relative humidity of from 70% to 100% isjetted out onto the surface of the wetted cellulose acetate film. As thecase may be, water on the surface of the film may be scraped away with arubber blade or the like, or the film may be contacted with a rollcovered with a water-absorbing cloth to thereby remove water from itssurface. These methods may be effected singly or may be combined. Ofthose, especially preferred is the method of using an air knife forwater removal from the film surface.

Preferably, the water removal from the film surface is carried out in acasing in which the atmosphere has a relative humidity of from 70% to100%. Also preferably, the temperature in the casing is controlled tofall between 60° C. and 150° C.

[Stretching Method]

The atmosphere in which the film is stretched may be any of air, watervapor or water.

Stretching in air means that the film is stretched in air of which thetemperature is specifically controlled but the humidity is not.Preferably, the stretching temperature falls between 50° C. and 150° C.,more preferably between 60° C. and 130° C., even more preferably between65° C. and 110° C.

Stretching in water vapor means that the film is exposed to anatmosphere having a constant temperature and a high humidity or to watervapor. Preferably, the stretching temperature falls between 50° C. and150° C., more preferably between 60° C. and 140° C., even morepreferably between 70° C. and 130° C. Also preferably, the relativehumidity in the water vapor atmosphere falls between 60% RH and 100% RH.In that condition, the water content of cellulose acetate to constitutethe film being stretched is kept between 2.0% by weight and 20.0% byweight. If the water content of the film being stretched is lower than2.0% by weight, the elongation at break thereof is low and the film isreadily broken, and, as a result, the retardation value Re550 of thestretched film measured at a wavelength of 550 nm could not reach λ/4.

Stretching in water means that the film is stretched while dipped inwater in a water tank. Preferably, the temperature of the water fallsbetween 50° C. and 100° C., more preferably between 60° C. and 98° C.,even more preferably between 65° C. and 95° C. Also preferably, thedipping time falls between 0.5 seconds and 10 minutes, more preferablybetween 1 second and 8 minutes, even more preferably between 1 secondand 7 minutes.

In stretching the film, the aspect ratio L/W preferably falls between0.05 and 4, more preferably between 0.1 and 3, even more preferablybetween 0.1 and 2, in which L indicates the distance between the fixingmembers by which the film to be stretched is fixed and W indicates thewidth of the film measured in the direction perpendicular to the fixingmember-to-fixing member distance.

Preferably, the water content of the film just after having beenstretched is kept still falling between 2.0% by weight and 20.0% byweight, since the film in that condition can be uniformly stretched.More preferably, it is kept falling between 2.1% by weight and 18.0% byweight, even more preferably between 2.2% by weight and 16.0% by weight.The water content of the non-stretched film just before the stretchingzone in which it is to be stretched is controlled to fall between 2.0%by weight and 20.0% by weight. Therefore, if the water content of thefilm just after having been stretched is lower than 2.0% by weight, theelongation at break of the stretched film will be low and the frontretardation of the film having a desired thickness could not reach theregion of λ/4.

The water content of the film just after having been stretched is meantto indicate the water content of the film just after the step ofstretching the film.

If desired, water having adhered to the stretched film maybe removedbefore the film is wound up. For this, employable is any known method ofusing an air knife, a blade or the like.

The film may be stretched in any direction of machine (longitudinal) ortransverse (width) direction. As the case may be, the film may bestretched in both the machine direction and the transverse direction.The machine direction means the direction in which the film runs throughthe stretching apparatus; and the transverse direction means thedirection that is perpendicular to the machine direction. Especiallypreferably, the film is monoaxially stretched in any of the machine ortransverse direction. More preferably, it is monoaxially stretched inthe machine direction.

Stretching the film may be effected in any known manner of, for example,zone stretching, roll stretching or tenter stretching. If desired, thefilm may be stretched between clips that clip it. In the method of usingclips for stretching the film therebetween, the two ends of therectangular film are clipped by fixing members such as clips so that thefilm does not slip, and the thus-fixed film is stretched. Also preferredis the method of stretching the film between rolls, in which the filmmay be stretched in one stage or in multiple stages. In this, the rollsmay be disposed in parallel to the film or may cross the film. The rollsare not specifically defined, for which, however, preferred are niprolls, jacket rolls and expander rolls. More preferred are nip rollsthat have the advantage of stretching stability.

Preferably, the draw ratio of the film being stretched falls 1.1 timesand 2.0 times, more preferably between 1.15 times and 1.9 times, evenmore preferably between 1.2 times and 1.8 times. The film may bestretched in one stage or in multiple stages. In case where the film isstretched in multiple stages, the product of the draw ratios in eachstage shall fall within the defined range.

The stretching speed may fall between 10%/min and 1000%/min, but morepreferably between 20%/min and 800%/min, even more preferably between30%/min and 700%/min.

Preferably, the stretching time falls between 1 and 30 seconds, morepreferably between 2 and 25 seconds, even more preferably between 3 and20 seconds.

Preferably, the thickness of the non-stretched film (film beforestretch) falls between 40 μm and 300 μm, more preferably between 45 μmand 280 μm, even more preferably between 50 μm and 250 μm. Alsopreferably the thickness of the stretched film (film after stretch)falls between 40 μm and 250 μm, more preferably between 50 μm and 230μm, even more preferably between 60 μm and 200 μm.

Preferably, the width of the non-stretched film falls between 5 cm and 3m, more preferably between 8 cm and 2.5 m, even more preferably between10 cm and 2 m.

The stretched film is preferably dried. The drying temperaturepreferably falls between 40° C. and 150° C., more preferably between 50°C. and 130° C., even more preferably between 60° C. and 120° C. Thedrying time preferably fall between 10 seconds and 20 minutes, morepreferably between 20 seconds and 10 minutes, even more preferablybetween 30 seconds and 7 minutes.

It is desirable that the stretched film is dried while it is conveyed tothe next stage. Preferably, the tension under which the film is conveyedfalls between 1 kg/m and 50 kg/m, more preferably between 3 kg/m and 30kg/m, even more preferably between 5 kg/m and 20 kg/m.

[Stretching Method with Nip Rolls]

The method of stretching the film with nip rolls is described in detailhereinunder.

At least two pairs, more preferably from 2 pairs to 8 pairs, even morepreferably from 2 pairs to 6 pairs of nip rolls are used for stretchingthe film.

The method of using two pairs of nip rolls is for one-stage stretching;and the method of using three or more pairs of nip rolls is formulti-stage stretching. A nip pressure is applied to the paired niprolls, and the cellulose acetate film to be stretched is passed betweenthe thus-pressured paired nip rolls while the rotation speed of one pairof roll is made different from that of the other. Thus having beenpassed through the paired nip rolls in that condition, the film isstretched. Concretely, the rotation speed of the nip roll on the outletside (on the downstream side) in the film-traveling direction is madehigher than that of the other nip roll on the inlet side (on theupstream side), and the film running through the nip rolls in thatcondition is stretched and drawn.

Two nip rolls are paired for stretching the film therebetween, and it isdesirable that one or both of them is/are covered with rubber. In theinvention, the water content of the film to be stretched is high and thefilm often slips while it is stretched. Therefore, rubber-coated rollsare preferred for stretching the film. The rubber material may be any ofnatural rubber or synthetic rubber (e.g., neoprene rubber,styrene-butadiene rubber, silicone rubber, urethane rubber, butylrubber, nitrile rubber, chloroprene rubber). Preferably, the thicknessof the rubber coating falls between 1 mm and 50 mm, more preferablybetween 2 mm and 40 mm, even more preferably between 3 mm and 30 mm.

Also preferably, the diameter of each nip roll falls between 5 cm and100 cm, more preferably between 10 cm and 50 cm, even more preferablybetween 15 cm and 40 cm.

Preferably, the nip rolls for use herein are hollow rolls of which thetemperature can be controlled in their hollow inside.

Regarding the roll-to-roll distance, it is desirable that the aspectratio L′/W′ satisfies 0.5≦L′/W′≦2, more preferably 0.7≦L′/W′≦1.8, evenmore preferably 0.9≦L′/W′≦1.6, in which W′ (cm) indicates the width ofthe cellulose acetate film and L′ (cm) indicates the distance betweenthe nip rolls. In case where three or more pairs of nip rolls are used,the ratios L′/W′ of every pair of rolls shall be averaged. In general,the aspect ratio of the nip rolls for film stretching is larger than 2.In the invention, it is a matter of importance that the aspect ratio ofthe nip rolls to be used is kept small while the water content of thefilm to be stretched between them is specifically controlled as definedherein, for optimizing the NZ factor of the stretched film.

The nip pressure to be applied to the nip rolls preferably falls between0.5 t/m width and 20 t/m width, more preferably between 1 t/m width and10 t/m width, even more preferably between 2 t/m width and 7 t/m width.

In case where the film is stretched between such nip rolls, thestretching temperature preferably falls between 50° C. and 150° C., morepreferably between 60° C. and 140° C., even more preferably between 70°C. and 130° C. In general, the temperature for film stretching isunified both in the transverse direction and in the machine direction.In the invention, however, it is desirable that the film-stretchingtemperature is not unified in at lease one direction. Preferably, thetemperature difference in stretching the film in the invention fallsbetween 1° C. and 20° C., more preferably between 2° C. and 17° C., evenmore preferably between 2° C. and 15° C.

The film having a specific water content as in the invention has alowered glass transition point (Tg), and it can be stretched even underlow tension. However, the film is often necked in while stretched, andit will be unevenly stretched. To solve the problem, a temperatureprofile of the film being stretched is effective, which is describedbelow.

(i) Temperature Profile in Machine Direction:

In film stretching with nip rolls, stress will often concentrate in theupstream nip roll outlet (this is the stretching start point), and thefilm locally receives too much stress in that site, and, as a result,the film could not often be stretched uniformly. Specifically, foruniformly stretching the film in the entire region in which the film isstretched, it is desirable that the temperature at the site immediatelyafter the upstream nip roll is made lower than the mean temperature inthe stretching zone (that is, the temperature in the center of thestretching zone in the machine direction) by the temperature differencementioned above. The temperature profile in stretching the film may beattained, for example, as follows: A temperature-controllable roll isused for the upstream nip roll and its temperature is lowered; or asplit heat source (e.g., radiation heat source such as IR heater, orheat jet with multiple jet mouths) is disposed along the film in itsmachine direction.

(ii) Temperature Profile in Transverse Direction:

The film having the aspect ratio mentioned above is often unevenlystretched in the transverse direction thereof. Specifically, both edgesof the film are more stretched than the center part thereof. To solvethe problem, therefore, it is desirable that the temperature of bothedges of the film being stretched is kept higher than that of the centerpart thereof in the transverse direction by the temperature differencementioned above. The temperature profile in stretching the film may beattained, for example, by disposing a split heat source (e.g., radiationheat source such as IR heater, or heat jet with multiple jet mouths)around the film in its transverse direction.

Preferably, the film is stretched between the nip rolls under thecondition as above, for a period of time falling between 1 and 30seconds, more preferably between 2 and 25 seconds, even more preferablybetween 3 and 20 seconds.

One embodiment of film stretching with nip rolls is describedhereinabove.

Other embodiments of film stretching in the invention are describedbelow, which may apply not only to nip rolls but also any others.

[Embodiments of Outline Constitution of Stretching Method]

FIG. 1 to FIG. 6 show the outline constitution of some embodiments ofthe stretching method employable in the invention. (In the followingdescription, the parenthesized numerals correspond to the numerals inthe drawings.) Of those, the constitution of FIG. 1 and FIG. 2 ispreferred; and the constitution of FIG. 2 is more preferred.

In FIG. 1, the film to be stretched is dipped in water to absorb waterand then stretched in water vapor. As illustrated, the film fed from afeed roll (1) is conveyed through a water tank (2), in which it absorbswater to have a water content as specifically defined herein. As somentioned hereinabove, it is desirable that the water in the tank isheated. Having passed through the water tank, the film is then led intoa stretching zone, in which the water film on the film surface is firstremoved by air knives (3), and then the film is stretched between twopairs of nip rolls (4).

Concretely, the rotation speed of the nip rolls on the winding-up side(on the outlet side) is kept higher than that of the nip rolls on thefeeding-out side (on the inlet side), whereby the film is stretched anddrawn between the nip rolls. In this stage, the stretching zone hassteam jet mouths (5), via which steam is jetted out thereinto and thehumidity in the stretching zone is kept within the range as above. Thestretching zone may have multiple steam jet mouths (5) set therein so asto further stabilize the humidity therein. As the case may be, a heater(not shown) may be disposed inside the stretching zone so as to controlthe temperature therein to a predetermined one. After thus stretched,the film is led through a drying zone (6) and then wound up around awind-up roll (7).

In FIG. 2 and FIG. 5, the film to be stretched is exposed to water vaporto absorb water and then stretched in water vapor. As illustrated, thefilm fed out from the roll is exposed to water vapor that jets outtoward it through jet mouths (9), and it absorbs water. The others arethe same as those in FIG. 1.

In FIG. 3, the film to be stretched is dipped in water to absorb waterand then stretched in water. Like in FIG. 1, the film is dipped in waterto absorb water, and then stretched between the nip rolls set in a watertank (8). Preferably, the water in the water tank is heated, as somentioned hereinabove. After thus stretched, the film is dried and woundup in the same manner as in FIG. 1.

In FIG. 4 and FIG. 6, the film to be stretched is exposed to water vaporto absorb water and then stretched in water. Like in FIG. 2, the film isprocessed to absorb water, and then this is stretched in the same manneras in FIG. 3. After thus stretched, the film is dried and wound up inthe same manner as in FIG. 1.

[Film Retardation]

The film retardation value (Re) is computed according to the followingequation:Retardation Value (Re)=(nx−ny)×dwherein nx indicates the refractive index along the slow axis in plainof the optical compensating film (the maximum refractive index in plainof the optical compensating film); ny indicates the refractive indexperpendicular to the slow axis in plane of the optical compensatingfilm, and d indicates the thickness (nm) of the optical compensatingfilm.

Preferably, the retardation measured at a wavelength of 550 nm, Re550 ofthe optical compensating film of the invention falls between 20 nm and2000 nm, more preferably between 40 nm and 500 nm, even more preferablybetween 80 nm and 300 nm.

Also preferably, the distribution of the retardation value measured at awavelength of 550 nm, Re550 of the optical compensating film is at most10% in both the transverse direction and the machine direction of thefilm.

In particular, in case where the optical compensating film of theinvention is used for a λ/4 plate, it is desirable that the retardationvalue measured at a wavelength of 450 nm (Re450) of the film fallsbetween 60 and 135 nm, the retardation value measured at a wavelength of590 nm (Re590) thereof falls between 100 and 170 nm, and the filmsatisfies Re590−Re450≧2 nm. More preferably, the film satisfiesRe590−Re450≧5 nm, most preferably Re590−Re450≧10 nm.

In case where the optical compensating film of the invention is used fora λ/2 plate, it is desirable that the retardation value measured at awavelength of 450 nm (Re450) of the film falls between 120 and 270 nm,the retardation value measured at a wavelength of 590 nm (Re590) thereoffalls between 200 and 340 nm, and the film satisfies Re590−Re450≧4 nm.More preferably, the film satisfies Re590−Re450≧10 nm, most preferablyRe590−Re450≧20 nm.

In any case of using the film for a λ/4 plate or λ/2 plate, it isdesirable that the retardation value measured at a wavelength of 450 nm,550 nm or 650 nm: Re450, Re550 and Re650 of the film satisfy thefollowing:0.5<Re450/Re550<0.98,1.01<Re650/Re550<1.35.More preferably,0.6<Re450/Re550<0.95,1.05<Re650/Re550<1.3.Even more preferably,0.7<Re450/Re550<0.9,1.1<Re650/Re550<1.25.[NZ Factor]

Preferably, the cellulose acetate film used singly in the inventionsatisfies the following equation:1≦(nx−nz)/(nx−ny)≦3wherein nx indicates the refractive index along the slow axis in plainof the optical compensating film, ny indicates the refractive indexperpendicular to the slow axis in plane of the optical compensatingfilm, and nz indicates the refractive index of the film in the directionof the thickness thereof.

In the invention, the NZ factor is a value indicated by (nx−nz)/(nx−ny).Preferably, the NZ factor falls between 1.1 and 2.8, more preferablybetween 1.2 and 2.7, even more preferably between 1.5 and 2.5.Satisfying the condition, the method of the invention produces betterresults.

[Haze]

The haze of the optical compensating film of the invention is computedaccording to the equation mentioned below, and it is preferably at most2.0%, more preferably at most 1.0%, most preferably at most 0.6%.Haze (HZ)=[diffusion (D)/total transmittance (T)]×100(%)wherein the diffusion (D) indicates the intensity of the light diffusedby the film, and this is measured with a haze meter; and the totaltransmittance (T) indicates the mean transmittance of visible light offrom 400 to 700 nm, through the film.

The optical compensating film of a cellulose acetate film having theabove-mentioned optical properties may be produced, using the materialsmentioned below.

[Retardation-Controlling Agent]

For controlling the retardation value of the film at differentwavelengths, it is desirable that a retardation-controlling agent isadded to cellulose acetate for the film.

Preferably, the amount of the retardation-controlling agent to be addedto cellulose acetate falls between 0.01 and 30 parts by weight relativeto 100 parts of cellulose acetate, more preferably between 0.05 and 25parts by weight, even more preferably between 0.1 and 20 parts byweight. If desired, two or more different types ofretardation-controlling agents may combined and used herein.

Preferably, the retardation-controlling agent for use herein has amaximum absorption wavelength in a wavelength range of from 210 to 360nm. Also preferably, the retardation-controlling agent does notsubstantially absorb visible light.

For the retardation-controlling agent, preferred are compounds having atleast two “aromatic rings”. The “aromatic ring” referred to hereinincludes aromatic hydrocarbon rings and aromatic hetero-rings.

Especially preferably, the aromatic hydrocarbon ring to be in thecompound for the agent is a 6-membered ring (i.e., benzene ring).

The aromatic hetero-rings are generally unsaturated hetero-rings, forwhich preferred are 5-membered, 6-membered and 7-membered rings. Morepreferred are 5-membered and 6-membered rings. The aromatic hetero-ringsgenerally have a largest number of double bonds. For the heteroatom inthese, preferred are nitrogen, oxygen and sulfur atoms; and morepreferred is a nitrogen atom. Examples of the aromatic hetero-ringsinclude furan, thiophene, pyrrole, oxazole, isoxazole, thiazole,isothiazole, imidazole, pyrazole, furazane, triazole, pyran, pyridine,pyridazine, pyrimidine, pyrazine and 1,3,5-triazine rings.

For the aromatic rings, for example, preferred are benzene, furan,thiophene, pyrrole, oxazole, thiazole, imidazole, triazole, pyridine,pyrimidine, pyrazine and 1,3,5-triazine rings.

Preferably, the number of such aromatic rings to be in the compound forthe retardation-controlling agent for use herein is from 2 to 20, morepreferably from 2 to 12, most preferably from 2 to 6.

The retardation-controlling agent of the type may be any of (α) tabularcompounds or (β) rod compounds mentioned below. One or more thesecompounds may be used either singly or as combined for the agent.

(α) Tabular Compounds:

The tabular compounds each contain at least two pairs of aromatic rings,in which the bonding mode of the two aromatic rings is grouped into (a)a case of forming a condensed ring, (b) a case of directly bonding toeach other via a single bond, and (c) a case of bonding to each othervia a linking group (however, the aromatic rings could not form a spirobond). In the compounds, the bonding mode of the aromatic rings may beany of (a) to (c).

Examples of the case (a) condensed ring (composed of at least twoaromatic rings) include indene, naphthalene, azulene, fluorene,phenanthrene, anthracene, acenaphthylene, biphenylene, naphthacene,pyrene, indole, isoindole, benzofuran, benzothiophene, indolidine,benzoxazole, benzothiazole, benzimidazole, benzotriazole, purine,indazole, chromene, quinoline, isoquinoline, quinolidine, quinazoline,cinnoline, quinoxaline, phthalazine, pteridine, carbazole, acridine,phenanthridine, xanthene, phenazine, phenothiazine, phenoxthine,phenoxazine and thianthrene rings. Of those, preferred are naphthalene,azulene, indole, benzoxazole, benzothiazole, benzimidazole,benzotriazole and quinoline rings.

The single bond in (b) is preferably a carbon-carbon bond that bonds twoaromatic rings. If desired, however, two or more single bonds may bondtwo aromatic rings to thereby form an aliphatic ring or a non-aromatichetero-ring between the thus-bonded two rings.

Also preferably, the linking group in (c) bonds to the carbon atoms oftwo aromatic rings. Preferred examples of the linking group are analkylene group, an alkenylene group, an alkynylene group, —CO—, —O—,—NH—, —S—, and their combinations. Some examples of combined linkinggroups are mentioned below, in which the right and left configurationsof the linking groups may be reversed.

-   c1: —CO—O—-   c2: —CO—NH—-   c3: -alkylene-O—-   c4: —NH—CO—NH—-   c5: —NH—CO—O—-   c6: —O—CO—O—-   c7: —O-alkylene-O—-   c8: —CO-alkenylene--   c9: —CO-alkenylene-NH—-   c10: —CO-alkenylene-O—-   c11: -alkylene-CO—O-alkylene-O—CO-alkylene--   c12: —O-alkylene-CO—O-alkylene-O—CO-alkylene-O—-   c13: —O—CO-alkylene-CO—O—-   c14: —NH—CO-alkenylene--   c15: —O—CO-alkenylene-

The aromatic rings and the linking groups may have substituents.

Examples of the substituents include a halogen atom (F, Cl, Br, I), ahydroxyl group, a carboxyl group, a cyano group, an amino group, a nitrogroup, a sulfo group, a carbamoyl group, a sulfamoyl group, an ureidogroup, an alkyl group, an alkenyl group, an alkynyl group, an aliphaticacyl group, an aliphatic acyloxy group, an alkoxy group, analkoxycarbonyl group, an alkoxycarbonylamino group, analkylthio group,an alkylsulfonyl group, an aliphatic amido group, an aliphaticsulfonamido group, an aliphatic substituted amino group, an aliphaticsubstituted carbamoyl group, an aliphatic substituted sulfamoyl group,an aliphatic substituted ureido group, and a non-aromatic heterocyclicgroup.

Preferably, the alkyl group has from 1 to 8 carbon atoms. For it, anacyclic alkyl group is preferred to a cyclic alkyl group, and a linearalkyl group is especially preferred. The alkyl group may be furthersubstituted (for example, with any of a hydroxyl group, a carboxylgroup, an alkoxy group and an alkyl-substituted amino group). Examplesof the alkyl group (including substituted alkyl groups) are methyl,ethyl, n-butyl, n-hexyl, 2-hydroxyethyl, 4-carboxybutyl, 2-methoxyethyland 2-diethylaminoethyl groups.

Preferably, the alkenyl group has from 2 to 8 carbon atoms. For it, anacyclic alkenyl group is preferred to a cyclic alkenyl group, and alinear alkenyl group is especially preferred. The alkenyl group may befurther substituted. Examples of the alkenyl group include vinyl, allyland 1-hexenyl groups.

Preferably, the alkynyl group has from 2 to 8 carbon atoms. For it, anacyclic alkynyl group is preferred to a cyclic alkynyl group, and alinear alkynyl group is especially preferred. The alkynyl group may befurther substituted. Examples of the alkynyl group include ethynyl,1-butynyl and 1-hexynyl groups.

Preferably, the aliphatic acyl group has from 1 to 10 carbon atoms.Examples of the aliphatic acyl group include acetyl, propanoyl andbutanoyl groups.

Preferably, the aliphatic acyloxy group has from 1 to 10 carbon atoms.One example of the aliphatic acyloxy group is an acetoxy group.

Preferably, the alkoxy group has from 1 to 8 carbon atoms. The alkoxygroup may be further substituted (for example, with an alkoxy group).Examples of the alkoxy group (including substituted alkoxy groups) aremethoxy, ethoxy, butoxy and methoxyethoxy groups.

Preferably, the alkoxycarbonyl group has from 2 to 10 carbon atoms.Examples of the alkoxycarbonyl group include methoxycarbonyl andethoxycarbonyl groups.

Preferably, the alkoxycarbonylamino group has from 2 to 10 carbon atoms.Examples of the alkoxycarbonylamino group include methoxycarbonylaminoand ethoxycarbonylamino groups.

Preferably, the alkylthio group has from 1 to 12 carbon atoms. Examplesof the alkylthio group include methylthio, ethylthio and octylthiogroups.

Preferably, the alkylsulfonyl group has from 1 to 8 carbon atoms.Examples of the alkylsulfonyl group include methanesulfonyl andethanesulfonyl groups.

Preferably, the aliphatic amido group has from 1 to 10 carbon atoms. Oneexample of the aliphatic amido group is an acetamido group.

Preferably, the aliphatic sulfonamido group has from 1 to 8 carbonatoms. Examples of the aliphatic sulfonamido group includemethanesulfonamido, butanesulfonamido and n-octanesulfonamido groups.

Preferably, the aliphatic substituted amino group has from 1 to 10carbon atoms. Examples of the aliphatic substituted amino group includedimethylamino, diethylamino and 2-carboxyethylamino group.

Preferably, the aliphatic substituted carbamoyl group has from 2 to 10carbon atoms. Examples of the aliphatic substituted carbamoyl groupinclude methylcarbamoyl and diethylcarbamoyl groups.

Preferably, the aliphatic substituted sulfamoyl group has from 1 to 8carbon atoms. Examples of the aliphatic substituted sulfamoyl groupinclude methylsulfamoyl and diethylsulfamoyl groups.

Preferably, the aliphatic substituted ureido group has from 2 to 10carbon atoms. One example of the aliphatic substituted ureido group us amethylureido group.

Examples of the non-aromatic heterocyclic group include piperidino andmorpholino groups.

Preferably, the molecular weight of the retardation-controlling agentfalls between 300 and 800. Specific examples of such tabularretardation-controlling agents are described, for example, inInternational Patent Laid-Open No. WO 00/65384.

(β) Rod Compounds:

In the invention, rod compounds having a maximum absorption in a shortwavelength range shorter than 250 nm are also preferred for theretardation-controlling agent.

In view of their function as the retardation-controlling agent, the rodcompounds for use herein preferably have at least one aromatic ring,more preferably at least two aromatic rings each.

Also preferably, the rod compounds have a linear molecular structure.The linear molecular structure is meant to indicate that the molecularstructure of the rod compound is linear when it is the most stable inpoint of its thermodynamic aspect. The structure of the compound that isthe most stable in point of its thermodynamic aspect can be determinedthrough crystal structure analysis or molecular orbital computation. Forexample, using a molecular orbital computation software (e.g.,WinMOPAC2000 from Fujitsu), the compound is analyzed through molecularorbital computation, and its molecular structure with which the heat offorming the compound is the smallest is determined. The linear molecularstructure is meant to indicate that the angle of the molecular structurethat has been found to be the most stable in point of its thermodynamicaspect through the computation as above is at least 140 degrees.

For the rod compounds for use herein, preferred are those of thefollowing formula (I):Ar¹-L¹-Ar²  (I)

In formula (I), Ar¹ and Ar² each independently represent an aromaticgroup.

In the present description, the aromatic group includes an aryl group(aromatic hydrocarbon group), a substituted aryl group, an aromaticheterocyclic group and a substituted aromatic heterocyclic group.

For it, aryl and substituted aryl groups are preferred to aromaticheterocyclic and substituted aromatic heterocyclic groups. Thehetero-ring in the aromatic heterocyclic group is generally unsaturated.Preferably, the aromatic hetero-ring is a 5-membered, 6-membered or7-membered ring, more preferably a 5-membered or 6-membered ring. Thearomatic hetero-ring generally has a largest number of double bonds. Forthe heteroatom in the ring, preferred is any of nitrogen, oxygen orsulfur atom, and more preferred is nitrogen or sulfur atom. Examples ofthe aromatic hetero-rings include furan, thiophene, pyrrole, oxazole,isoxazole, thiazole, isothiazole, imidazole, pyrazole, furazane,triazole, pyran, pyridine, pyridazine, pyrimidine, pyrazine and1,3,5-triazine rings.

Preferred examples of the aromatic ring for the aromatic group arebenzene, furan, thiophene, pyrrole, oxazole, thiazole, imidazole,triazole, pyridine, pyrimidine and pyrazine rings; and more preferredfor it is a benzene ring.

Examples of the substituents for the substituted aryl group and thesubstituted aromatic heterocyclic group include a halogen atom (F, Cl,Br, I), a hydroxyl group, a carboxyl group, a cyano group, an aminogroup, an alkylamino group (e.g., methylamino, ethylamino, butylamino,dimethylamino), a nitro group, a sulfo group, a carbamoyl group, analkylcarbamoyl group (e.g., N-methylcarbamoyl, N-ethylcarbamoyl,N,N-dimethylcarbamoyl), a sulfamoyl group, an alkylsulfamoyl group(e.g., N-methylsulfamoyl, N-ethylsulfamoyl, N,N-dimethylsulfamoyl), anureido group, an alkylureido group (e.g., N-methylureido,N,N-dimethylureido, N,N,N′-trimethylureido), an alkyl group (e.g.,methyl, ethyl, propyl, butyl, pentyl, heptyl, octyl, isopropyl, s-butyl,t-amyl, cyclohexyl, cyclopentyl), analkenyl group (e.g., vinyl, allyl,hexenyl), an alkynyl group (e.g., ethynyl, butynyl), an acyl group(e.g., formyl, acetyl, butyryl, hexanoyl, lauryl), an acyloxy group(e.g., acetoxy, butyryloxy, hexanoyloxy, lauryloxy), an alkoxy group(e.g., methoxy, ethoxy, propoxy, butoxy, pentyloxy, heptyloxy,octyloxy), an aryloxy group (e.g., phenoxy), an alkoxycarbonyl (e.g.,methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl,pentyloxycarbonyl, heptyloxycarbonyl), an aryloxycarbonyl group (e.g.,phenoxycarbonyl), an alkoxycarbonylamino group (e.g.,butoxycarbonylamino, hexyloxycarbonylamino), an alkylthio group (e.g.,methylthio, ethylthio, propylthio, butylthio, pentylthio, heptylthio,octylthio), an arylthio group (e.g., phenylthio), an alkylsulfonyl group(e.g., methylsulfonyl, ethylsulfonyl, propylsulfonyl, butylsulfonyl,pentylsulfonyl, heptylsulfonyl, octylsulfonyl), an amido group (e.g.,acetamido, butylamido, hexylamido, laurylamido), and a non-aromaticheterocyclic group (e.g., morpholyl, pyrazinyl).

For the substituents for the substituted aryl group and the substitutedaromatic heterocyclic group, preferred are a halogen atom, a cyanogroup, a carboxyl group, a hydroxyl group, an amino group, analkyl-substituted amino group, an acyl group, an acyloxy group, an amidogroup, an alkoxycarbonyl group, an alkoxy group, an alkylthio group andan alkyl group.

The alkyl moiety in the alkylamino group, the alkoxycarbonyl group, thealkoxy group and the alkylthio group, and also the alkyl group may befurther substituted. Examples of the substituents for the alkyl moietyand the alkyl group include a halogen atom, a hydroxyl group, a carboxylgroup, a cyano group, an amino group, an alkylamino group, a nitrogroup, a sulfo group, a carbamoyl group, an alkylcarbamoyl group, asulfamoyl group, an alkylsulfamoyl group, an ureido group, analkylureido group, an alkenyl group, an alkynyl group, an acyl group, anacyloxy group, an alkoxy group, an aryloxy group, an alkoxycarbonylgroup, an aryloxycarbonyl group, an alkoxycarbonylamino group, analkylthio group, an arylthio group, an alkylsulfonyl group, an amidogroup and a non-aromatic heterocyclic group. For the substituents forthe alkyl moiety and the alkyl group, preferred are a halogen atom, ahydroxyl group, an amino group, an alkylamino group, an acyl group, anacyloxy group, an acylamino group, an alkoxycarbonyl group and an alkoxygroup.

In formula (I), L¹ represents a divalent linking group selected from analkylene group, an alkenylene group, an alkynylene group, —O—, —CO— andtheir combinations.

The alkylene group may have a cyclic structure. The cyclic alkylenegroup is preferably a cyclohexylene group, more preferably a1,4-cyclohexylene group. For the acyclic alkylene group, a linearalkylene group is preferred to a branched alkylene group.

Preferably, the alkylene group has from 1 to 20 carbon atoms, morepreferably from 1 to 15 carbon atoms, even more preferably from 1 to 10carbon atoms, still more preferably from 1 to 8 carbon atoms, mostpreferably from 1 to 6 carbon atoms.

Preferably, the alkenylene group and the alkynylene group have anacyclic structure but not a cyclic structure. More preferably, they havea linear structure but not a branched structure.

Also preferably, the alkenylene group and the alkynylene group have from2 to 10 carbon atoms, more preferably from 2 to 8 carbon atoms, evenmore preferably from 2 to 6 carbon atoms, still more preferably from 2to 4 carbon atoms each. Most preferred is a 2-vinylene (or ethynylene)group.

Examples of the combined, divalent linking groups are mentioned below.

-   L-1: —O—CO-alkylene-CO—O—-   L-2: —CO—O-alkylene-O—CO—-   L-3: —O—CO-alkenylene-CO—O—-   L-4: —CO—O-alkenylene-O—CO—-   L-5: —O—CO-alkynylene-CO—O—-   L-6: —CO—O-alkynylene-O—CO—

In the molecular structure of formula (I), it is desirable that theangle at which Ar¹ meets Ar² via L¹ therebetween is at least 140degrees.

More preferably, the rod compounds for use herein are those of thefollowing formula (II):Ar¹-L²-X-L³-Ar²  (II)

In formula (II), Ar¹ and Ar² each independently represent an aromaticgroup. The definition and the examples of the aromatic group are thesame as those mentioned hereinabove for Ar¹ and Ar² in formula (I).

In formula (II), L² and L³ each independently represent a divalentlinking group selected from an alkylene group, —O—, —CO—, and theircombinations.

Preferably, the alkenylene group has an acyclic structure but not acyclic structure. More preferably, it has a linear structure but not abranched structure.

Also preferably, the alkenylene group has from 1 to 10 carbon atoms,more preferably from 1 to 8 carbon atoms, even more preferably from 1 to6 carbon atoms, still more preferably from 1 to 4 carbon atoms, mostpreferably 1 or 2 carbon atoms (methylene or ethylene).

Especially preferably, L² and L³ each are —O—CO— or —CO—O—.

In formula (II), X represents a 1,4-cyclohexylene, vinylene orethynylene group.

Specific examples of the compounds of formula (I) are mentioned below.

Compounds (1) to (34), (41) and (42) each have two asymmetric carbonatoms at the 1- and 4-positions of the cyclohexane ring therein.However, since compounds (1), (4) to (34), (41) and (42) have asymmetric meso-type molecular structure, they do not include opticalisomers (with optical activity) but have only geometric isomers (trans-and cis-isomers). 1-trans and 1-cis structures of compound (1) are shownbelow.

As so mentioned hereinabove, the rod compounds for use herein preferablyhave a linear molecular structure. Accordingly, trans-isomers arepreferred to cis-isomers of the compounds.

Compounds (2) and (3) have both geometric isomers and optical isomers(totaling four isomers). Of the geometric isomers thereof, trans-isomersare preferred to cis-isomers. However, there is no specific differencebetween the optical isomers of the compounds in point of theirsuperiority. The optical isomers may be any of D- or L-isomers or evenracemates.

In compounds (43) to (45), the center vinylene bond includes trans-andcis-structures. For the same reason as above, trans-structures are alsopreferred to cis-structures of these compounds.

Two or more different types of such rod compounds of which the maximumabsorption wavelength (λmax) is shorter than 250 nm in solution UVabsorptiometry may be combined and used in the invention.

The rod compounds may be produced with reference to the methodsdescribed in literature. The literature disclosing the methods includes,for example, Mol. Cryst. Liq. Cryst., Vol. 53, p. 229 (1979); ibid.,Vol. 89, p. 93 (1982); ibid., Vol. 145, p. 111 (1987); ibid., Vol. 170,p. 43 (1989); J. Am. Chem. Soc., Vol. 113, p. 1349 (1991); ibid., Vol.118, p. 5346 (1886); ibid., Vol. 92, p. 1582 (1970); J. Org. Chem., Vol.40, p. 420 (1875); Tetrahedron, Vol. 48, No. 16, p. 3437 (1992).

(Spectrometry of Retardation-Controlling Compounds)

The UV and visible range (UV-vis) spectrum of the above-mentionedretardation-controlling agent (10-trans) was measured. Concretely, theretardation-controlling agent (10-trans) was dissolved intetrahydrofuran (not containing a stabilizer, BHT (butylatedhydroxytoluene)) to prepare its solution having a concentration of 10⁻⁵mol/dm³. The resulting solution was measured with a spectrophotometer(from Hitachi), and the wavelength at which the solution showed amaximum absorption (λmax) was 220 nm. The absorption coefficient (ε) ofthe compound solution was 15000. In the same manner as above, theretardation-controlling agent (29-trans) was analyzed, and thewavelength at which the compound solution showed a maximum absorption(λmax) was 240 nm. The absorption coefficient (ε) of the compoundsolution was 20000. Also in the same manner, the retardation-controllingagent (41-trans) was analyzed, and the wavelength at which the compoundsolution showed a maximum absorption (λmax) was 230 nm. The absorptioncoefficient (ε) of the compound solution was 16000.

One or more retardation-controlling compounds may be used in theinvention, either singly or as combined.

[Production of Cellulose Acetate Film]

The cellulose acetate film for use in the invention is preferablyproduced in a solvent-casting method. In the solvent-casting method, thepolymer material for the film is dissolved in an organic solvent and theresulting solution (dope) is cast to form the intended polymer film.

One example of the method of producing the cellulose acetate film of theinvention is described concretely, using cellulose acetate.

The organic solvent is preferably selected from ethers having from 3 to12 carbon atoms, ketones having from 3 to 12 carbon atoms, esters havingfrom 3 to 12 carbon atoms, and halogenohydrocarbons having from 1 to 6carbon atoms.

These ethers, ketones and esters may have a cyclic structure. Compoundshaving at least two functional groups of ethers, ketones and esters(i.e., —O—, —CO— and —COO—) may also be used for the organic solvent.The organic solvent for use herein may have any other functional groupsuch as an alcoholic hydroxyl group. The number of carbon atoms thatconstitute the organic solvent having two or more functional groupsshall fall within the defined range of the compounds having any one ofthe functional groups.

Examples of the ethers having from 3 to 12 carbon atoms includediisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane,1,3-dioxolane, tetrahydrofuran, anisole and phenetole.

Examples of the ketones having from 3 to 12 carbon atoms includeacetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone,cyclohexanone and methylcyclohexanone.

Examples of the esters having from 3 to 12 carbon atoms include ethylformate, propyl formate, pentyl formate, methyl acetate, ethyl acetateand pentyl acetate.

Examples of the organic solvent having two or more functional groupsinclude 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.

Preferably, the halogenohydrocarbons for the organic solvent have 1 or 2carbon atoms, most preferably one carbon atom. The halogen in thehalogenohydrocarbons is preferably chlorine. Preferably, the degree ofhydrogen substitution with halogen in the halogenohydrocarbons fallsbetween 25 and 75 mol %, more preferably between 30 and 70 mol %, evenmore preferably between 35 and 65 mol %, most preferably between 40 and60 mol %. One typical example of the halogenohydrocarbons is methylenechloride.

Two or more different organic solvents may be mixed and used herein.

A cellulose acetate solution may be prepared in any ordinary manner. Theordinary manner is meant to indicate that the solution is prepared at atemperature not lower than 0° C. (room temperature or high temperature).For preparing the solution, employable are any known method and devicethat are generally used in preparing dopes in an ordinarysolvent-casting method. In the ordinary method, a halogenohydrocarbon(especially methylene chloride) is preferably used for the organicsolvent.

The amount of cellulose acetate to be dissolved in the organic solventis so controlled that the resulting solution has a cellulose acetatecontent of from 10 to 40% by weight. More preferably, the celluloseacetate content of the solution falls between 10 and 30% by weight. Anyoptional additive that will be mentioned hereinunder may be added to theorganic solvent (main solvent).

The intended solution may be prepared by stirring cellulose acetate inthe organic solvent at room temperature (0 to 40° C.). The solution ofhigh concentration may be stirred under heat and pressure. Concretely,cellulose acetate and the organic solvent are put into a pressure vesseland sealed up therein, and these are stirred under pressure while heatedat a temperature not lower than the boiling point at room temperature ofthe solvent but at which the solvent does not boil. The heatingtemperature is generally 40° C. or higher, preferably falling between 60and 200° C., more preferably between 80 and 110° C.

The individual components may be put into the vessel after they areroughly pre-mixed. Alternatively, they may be put thereinto one afteranother. The vessel must be so constituted that it allows the contentsto be stirred therein. An inert vapor such as nitrogen gas may beintroduced into the vessel to increase the pressure in the vessel. Forthe pressure increase, the increased vapor pressure of the heatedsolvent may also be utilized. As the case may be, after the vessel issealed up, the components may be forced thereinto under pressure.

Preferably, the vessel with the components therein is heated by anexternal heating unit. For it, for example, usable is a jacket heater.Alternatively, a plate heater may be provided outside the vessel, and aliquid is circulated therein so as to entirely heat the vessel.

Preferably, a stirring blade is disposed inside the vessel, with whichthe contents of the vessel may be stirred. It is desirable that thestirring blade is so long as to reach near the inner wall of the vessel.Also preferably, the end edges of the stirring blade are provided with ascraper that serves to renew the liquid film formed on the inner wall ofthe vessel.

If desired, the vessel may be equipped with some meters such as apressure gauge and a thermometer. In the vessel, the components aredissolved in the solvent. The dope thus prepared is taken out after ithas been cooled in the vessel; or after directly taken out of thevessel, it may be cooled with a heat exchanger or the like.

The solution may also be prepared in a cooling dissolution method. Inthe cooling dissolution method, cellulose acetate can be dissolved evenin an organic solvent in which it is difficult to dissolve in anordinary dissolving method. For the organic solvent for celluloseacetate, methylene chloride is generally used. However, methylenechloride is not good for global environment protection and for workingenvironment protection, and it is undesirable to use it. In an organicsolvent system not containing methylene chloride, cellulose acetate isdifficult to dissolve in an ordinary dissolving method. For that system,the cooling dissolution method is effective. Even for other solvents inwhich cellulose acetate can be dissolved in an ordinary dissolvingmethod, the cooling dissolution method is also effective as it rapidlyproduces a uniform solution.

In the cooling dissolution method, cellulose acetate is first graduallyadded to an organic solvent at room temperature with stirring.

Preferably, the amount of cellulose acetate to be added is so controlledthat the resulting mixture may contain from 10 to 40% by weight, morepreferably from 10 to 30% by weight of cellulose acetate. If desired,any optional additive that will be mentioned hereinunder may be added tothe mixture.

Next, the mixture is cooled to a temperature falling between −100° C.and −10° C., preferably between −80° C. and −10° C., more preferablybetween −50° C. and −20° C., most preferably between −50 and −30° C.Cooling it may be effected, for example, in a dry ice/methanol bath(−75° C.) or in a cooled diethylene glycol solution (from −30 to −20°C.). Thus cooled, the mixture of cellulose acetate and the organicsolvent is solidified.

Preferably, the cooling rate is at least 4° C./min, more preferably atleast 8° C./min, most preferably at least 12° C./min. Higher coolingrate is better, but the theoretical uppermost limit of the cooling rateis 10000° C./sec, the technical uppermost limit thereof is 1000° C./sec,and the practical uppermost limit thereof is 100° C./sec. The coolingrate is obtained by dividing the difference between the temperature atwhich the cooling is started and the final cooling temperature by thetime taken by the process to reach the final cooling temperature fromthe start of cooling.

Then, the thus-cooled mixture is heated up to a temperature fallingbetween 0° C. and 200° C., preferably between 0° C. and 150° C., morepreferably between 0° C. and 120° C., most preferably between 0° C. and50° C., through which cellulose acetate dissolves in the organicsolvent. Heating the mixture may be effected merely by leaving it atroom temperature, or the mixture may be heated in a hot bath.

Preferably, the heating rate is at least 4° C./min, more preferably atleast 8° C./min, most preferably at least 12° C./min. Higher heatingrate is better, but the theoretical uppermost limit of the heating rateis 10000° C./sec, the technical uppermost limit thereof is 1000° C./sec,and the practical uppermost limit thereof is 100° C./sec. The heatingrate is obtained by dividing the difference between the temperature atwhich the heating is started and the final heating temperature by thetime taken by the process to reach the final heating temperature fromthe start of heating.

A uniform solution of cellulose acetate can be obtained according to themethod as above. If cellulose acetate dissolution is still insufficient,the operations of cooling and heating may be repeated. Whether thedissolution is sufficient or not can be judged only by visuallyobserving the external appearance of the solution.

In the cooling dissolution method, it is preferred to use a closedvessel so that water from dew formation in cooling the mixture does notenter the mixture. In the cooling and heating process, pressureapplication during cooling and pressure reduction during heating resultin the reduction in the period of time taken for dissolution. Forpressure application and pressure reduction, preferred is a pressurevessel.

It has been confirmed through differential scanning calorimetry (DSC)that the 20 wt. % solution obtained by dissolving cellulose acetate(degree of acetylation: 60.9%, viscosity-average degree ofpolymerization: 299) in methyl acetate in the cooling dissolution methodhas a pseudo phase transition point of around 33° C. at which itundergoes sol-gel change. At a temperature lower than the pseudo phasetransition point, the solution forms a uniform gel. Accordingly, thesolution must be kept at a temperature not lower than the pseudo phasetransition point, preferably at a temperature higher than the pseudophase transition point by about 10° C. However, the pseudo phasetransition point of the solution varies depending upon the degree ofacetylation and the viscosity-average degree of polymerization ofcellulose acetate in the solution, and on the solution concentration andthe organic solvent used.

A cellulose acetate film is formed from the thus-prepared celluloseacetate solution (dope) in a solvent casting method.

A film is formed by casting the dope on a drum or a band and evaporatingthe solvent from it. Preferably, the dope to be cast is so controlledthat its solid content falls between 18 and 35% by weight. The surfaceof the drum or the band is preferably finished to have a mirror surface.The methods of casting and drying the film in the solvent casting methodare disclosed in U.S. Pat. Nos. 2,336,310, 2,367,603, 2,492,078,2,492,977, 2,492,978, 2,607,704, 2,739,069, 2,739,070; British Patents640,731, 736,892; JP-B 4554/1970, 5614/1974; JP-A 176834/1985,203430/1985, 115035/1987.

It is preferred to cast the dope on a drum or a band having a surfacetemperature not higher than 10° C. It is also preferred to dry the castdope by applying thereto wind for at least 2 seconds. The formed filmmay be peeled from the drum or the band and may be further dried byapplying thereto high-temperature wind that gradually varies from 100 to160° C. to thereby evaporate away the remaining solvent. This method isdisclosed in JP-B 17844/1993. According to these methods, the time to betaken from casting the solution to peeling off the film can be reduced.In this method, it is necessary that the dope should gel at the surfacetemperature of the drum or the band on which it is cast.

One or more films may be formed by casting the cellulose acetatesolution (dope) prepared in the above, according to the solvent castingmethod. For this, the dope is cast on a drum or a band, and the solventis evaporated away to form the intended film. Before cast, the dope ispreferably so controlled that its solid content falls between 10 and40%. Also preferably, the surface of the drum or the band ismirror-finished.

In case where at least two cellulose acetate solutions for at least twofilms are cast, the cellulose acetate solutions are cast on a supportthrough the respective casting mouths that are provided at intervals inthe machine direction of the support to thereby laminate the resultingfilms on the support. For this, for example, herein employable are themethods described in JP-A 158414/1986, 122419/1989, 198285/1999. Thecellulose acetate solution may be cast through two casting mouths toform the film. For this, for example, herein employable are the methodsdescribed in JP-B 27562/1985; JP-A 94724/1986, 94725/1986, 104813/1986,158413/1986, 134933/1994. A part from these, the casting methoddescribed in JP-A 162617/1981 is also employable herein, in which theflow of a high-viscosity cellulose acetate solution is enveloped in alow-viscosity cellulose acetate solution and the two, high-viscosity andlow-viscosity cellulose acetate solutions are co-extruded out to form acellulose acetate film.

Alternatively, two casting mouths may be used for film formation in sucha manner that the film formed on a support through the first castingmouth is peeled off and another film is formed through the secondcasting mouth on the thus-peeled film on its surface that was contactedwith the support, for example as in JP-B 20235/1969.

The same or different cellulose acetate solutions may be cast in filmformation with no specific limitation. To make the formed multiplecellulose acetate films have the respective functions, the celluloseacetate solutions capable of giving the intended functions to the filmsshall be extruded out through the respective casting mouths.

If desired, the cellulose acetate solution may be co-cast along with anyother solutions for other functional layers (e.g., adhesive layer,colorant layer, antistatic layer, antihalation layer, UV-absorbentlayer, polarizing layer) to form a laminate film.

In forming a single-layered film, it is necessary to extrude ahigh-concentration and high-viscosity cellulose acetate solution inorder that the film formed may have a desired thickness. In that case,however, the cellulose acetate solution is not stable and often forms asolid. This is problematic in that the solid causes fish eyes in thefilm formed, and the surface of the film is not smooth. To solve theproblem, multiple cellulose acetate solutions are cast through a castingmouth, and the resulting high-viscosity cellulose acetate solution isextruded onto a support to give a smooth and good film. Anotheradvantage is that the high-viscosity cellulose acetate solution reducesthe load of drying the film formed of it and its film-producing speedincreases.

A plasticizer may be added to the cellulose acetate film for improvingthe mechanical properties of the film and for rapidly drying the film.For the plasticizer, usable are phosphates or carboxylates. Examples ofthe phosphates include triphenyl phosphate (TPP), biphenyldiphenylphosphate (BDP) and tricresyl phosphate (TCP). The carboxylates aretypically phthalates and citrates. Examples of the phthalates includedimethyl phthalate (DMP), diethyl phthalate (EDP), dibutyl phthalate(DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) anddiethylhexyl phthalate (DEHP). Examples of the citrates include triethylo-acetylcitrate (OACTE) and tributyl o-acetylcitrate (OACTB). Examplesof other carboxylates include butyl oleate, methylacetyl ricinoleate,dibutyl sebacate, and various trimellitates. Phthalate plasticizers(DMP, DEP, DBP, DOP, DPP, DEHP) are preferred for use herein. Morepreferred are DEP and DPP.

The amount of the plasticizer that may be added to the film preferablyfalls between 0.1 and 25% by weight of cellulose acetate, morepreferably between 1 and 20% by weight, most preferably between 3 and15% by weight.

Also if desired, an anti-aging agent (e.g., antioxidant,peroxide-degrading agent, radical inhibitor, metal inactivator, acidscavenger, amine) may be added to the cellulose acetate film. Suchanti-aging agents are described in JP-A199201/1991, 197073/1993,194789/1993, 271471/1993, 107854/1994. The amount of the anti-agingagent that may be added to the film preferably falls between 0.01 and 1%by weight of the film-forming solution (dope), more preferably between0.01 and 0.2% by weight. If its amount is smaller than 0.01% by weight,the anti-aging agent will be almost ineffective. However, if its amountis larger than 1% by weight, the anti-aging agent will bleed out of thefilm surface. Especially preferred examples of the anti-aging agent foruse herein are butylated hydroxytoluene (BHT) and tribenzylamine (TBA).

One or both surfaces of the cellulose acetate film may be coated with amat layer that comprises a matting agent and a polymer, for improvingthe handlability of the film being produced. For the matting agent andthe polymer, preferred are the materials described in JP-A 44327/1998.If desired, the matting agent may be added to the dope.

Many other additives may also be added to the cellulose acetatesolution, if desired, in any stage before or after or during itspreparation. The additives include, for example, UV absorbents; fineinorganic particles of, for example, silica, kaolin, talc, diatomaceousearth, quartz, calcium carbonate, barium sulfate, titanium oxide oralumina; thermal stabilizers such as alkaline earth metal salts with,for example, calcium or magnesium; other antistatic agents, flameretardants, lubricants, and oils.

Also if desired, a release promoter may be added to the film forreducing the load necessary in peeling the film. For it, for example,surfactants are effective, including, for example, phosphates,sulfonates, carboxylates, nonionic surfactants and cationic surfactants,to which, however, the release promoter usable herein is not limited.These are described, for example, in JP-A 243837/1986.

[Surface Treatment of Cellulose Acetate Film]

The cellulose acetate film may undergo surface treatment. Concretely,for it, the film is subjected to corona discharge treatment, glowdischarge treatment, flame treatment, acid treatment, alkali treatmentor UV irradiation.

For ensuring the surface smoothness of the cellulose acetate film thatundergoes such surface treatment, it is desirable that the temperatureat which the film receives the treatment is not higher than the glasstransition point (Tg) of the film.

In case where the film is used for a transparent protective film ofpolarizing plates, it is especially desirable that the film receivesacid or alkali treatment for increasing its adhesiveness to thepolarizing film of the plates. More preferably, the film receives alkalitreatment.

One preferred cycle of alkali treatment of the film comprises dippingthe film in an alkali solution, then neutralizing it in an acidsolution, rinsing it in water, and drying it.

The alkali solution may be a potassium hydroxide solution or a sodiumhydroxide solution. Of the solution, the hydroxide ion normalityconcentration preferably falls between 0.1 N and 3.0 N, more preferablybetween 0.5 N and 2.0 N. Preferably, the temperature of the alkalisolution falls between room temperature and 90° C., more preferablybetween 40° C. and 70° C. The alkali solution may be an aqueous solutionor a solution in an organic solvent. For the latter, the organic solventis preferably a lower alcohol, more preferably an alcohol having from 1to 5 carbon atoms or a glycol, even more preferably ethanol, n-propanol,iso-propanol, butanol, ethylene glycol or propylene glycol. Still morepreferred are iso-propanol and propylene glycol. If desired, these maybe mixed for use herein. In addition, water or surfactant may be addedto the solvent.

Some preferred examples of the solvent in which alkali is dissolved tobe an alkali solution are mentioned below.

-   iso-propanol/propylene glycol/water (70/15/15, by volume)-   iso-propanol/water (85/15, by volume)-   iso-propanol/propylene glycol (85/15, by volume)-   iso-propanol alone

The film may be dipped in the alkali solution, or may be coated with it(for example, through bar coating or curtain coating).

In the invention, for improving the adhesiveness of the celluloseacetate film to the layer that overlies it (e.g., adhesive layer,orientation film, optical anisotropic layer), an adhesive layer (subbinglayer) may be provided on the film, for example, as in JP-A 333433/1995.Preferably, the thickness of the adhesive layer falls between 0.1 μm and2 μm, more preferably between 0.2 μm and 1 μm.

[Polarizing Plate]

A polarizing plate comprises a polarizing film and two transparentprotective films provided on both surfaces of the polarizing film. Inthis, one protective film may be the cellulose acetate film mentionedabove or may be the optical compensating film of the invention. Theother protective film may be an ordinary cellulose acetate film; or boththe protective films may be ordinary cellulose acetate films.

The polarizing film is, for example, an iodine-containing polarizingfilm, a dichromatic dye-containing polarizing film, or a polyenepolarizing film. For producing the iodine-containing polarizing film andthe dye-containing polarizing film, generally used are polyvinyl alcoholfilms.

The polymer films for these polarizing films are prepared, for example,as follows: Using a tenter-type stretching machine, a polymer film isstretched under the condition that satisfies the following requirement(1) while it keeps its self-sustainability and while its volatilecontent is still at least 5%, and after thus stretched, the film is thenshrunk to reduce its volatile content.|L2−L1|>0.4W  (1)wherein L1 indicates the trajectory of the film holder from thesubstantial holding start point of one edge of the film to thesubstantial holding release point thereof; L2 indicates the trajectoryof the film holder from the substantial holding start point of the otheredge of the film to the substantial holding release point thereof; and Windicates the distance between the two substantial holding releasepoints.

FIG. 7 is a schematic plan view showing a device for obliquelystretching a polymer film into a polarizing film of 45°-obliqueorientation. In this, (a) is a step of introducing an original polymerfilm 25 in the direction of the arrow (Y); (b) is a step of stretchingthe film in the transverse direction; and (c) is a step of conveying thethus-stretched film 26 to the subsequent step in the direction of thearrow (X). The film to be oriented is continuously introduced into thedevice in the direction (Y), and it is first held by the left-side (seenfrom the upstream side) holder at the point B1 (27′). In this stage, theother edge of the film is not held by the holder, and therefore the filmreceives no tension in the transverse direction thereof. In other words,the point B1 is not a substantial holding start point. The substantialholding start point is defined as the point at which both edges of thefilm are held by the holder, and this includes two points A1 (27) andC1, or that is, the downstream holding start point A1 and the point C1at which a runs approximately perpendicularly to the center line 21 ofthe traveling film from the point A1 meets the trajectory 23 of theholder on the opposite side. Starting from this point, when the film isconveyed through the holder substantially in such a manner that its bothedges run substantially at the same speed, then the point A1time-dependently moves to A2, A3, . . . An, and the point C1 alsotime-dependently moves to C2, C3, . . . Cn. In this stage, the travelingfilm passes through the corresponding points An and Cn that are thebases of the holder at the same time, and the line that connects An toCn is the orientation direction of the film in which the film isoriented in that stage at An and Cn. As in FIG. 7, the points An aregradually delayed from the points Cn, and the orientation direction istherefore gradually inclined from the direction perpendicular to themachine direction. The substantial holding release point includes twopoints Cx (28′) and Ay, or that is, the upstream point Cx at which thefilm separates from the holder and the point Ay at which a line thatruns approximately perpendicularly to the center line 22 of thetraveling film from the point Cx meets the trajectory 24 of the holderon the opposite side. The angle of the final orientation of thethus-stretched film is defined by the ratio of the pathway differencebetween the right and left sides of the holder at the end point of thestretching process, Ay−Ax (that is, |L2−L2|) to the substantial outletwidth, Ay−Cx (that is, W). The tilt angle θ of the film orientationdirection to the film-traveling direction is represented by thefollowing:tan θ=(Ay−Cx)/(Ay−Ax), or that is,tan θ=W/|L1−L2|.

After the point Ay, the upper edge of the film in the drawing is stillkept as it is up to 28. However, since the other edge of the film is notheld in this condition, the film is no more stretched in the transversedirection thereof and the point 28 is not a substantial holding releasepoint.

As in the above, the substantial holding start point is not a point atwhich each edge of the film is merely engaged with the correspondingside of the holder, but it includes two points. One is a downstreamsubstantial engaging point, and the other is so defined that the linewhich connects the two substantial holding start points meets the centerline of the traveling film approximately perpendicularly thereto at thatpoint. Similarly, the substantial holding release point includes two.One is an upstream substantial release point, and the other is sodefined that the line which connects the two substantial holding releasepoints meets the centerline of the traveling film approximatelyperpendicularly thereto at that point. The condition that the line meetsthe center line of the traveling film approximately perpendicularlythereto is meant to indicate that the line that connects the twosubstantial holding start points or the two substantial holding releasepoints meets the center line of the film at an angle of 90±0.5°therebetween.

In case where the holder in the tenter-type stretching machine is madeto have a pathway difference between the right and left sides thereof,the site at which both edges of the traveling film are first held by theholder on both sides thereof, or the site at which both edges of thestretched film are finally released from the holder on both sidesthereto to the next stage often have a position error in the machinedirection owing to some mechanical limitation, for example, on the raillength of the machine. However, so far as the pathway from thesubstantial holding start point to the substantial holding release pointdefined as above satisfies the requirement (1), the film to be stretchedin the machine enjoys any desired position tolerance.

The tilt angle of the orientation axis of the stretched film obtained inthe above can be controlled, depending on the ratio of the substantialpathway difference between the right and left sides of the holder at theend point of the stretching process, |L1−L2|, to the outlet width, W, inthe step (c). Polarizing plates and phase-shift films often require afilm of 45°-orientation relative to the machine direction. For orientinga film to have an orientation angle of around 45°, the film stretchingparameters preferably satisfy 0.9W<|L1−L2|<1.1W, more preferably0.97W<|L1−L2|<1.03W.

In reflection or transmission liquid crystal displays, the orientedcellulose acetate film is preferably so disposed that its phase lag axiscrosses the transmission axis of the polarizing film thereinsubstantially at an angle of 45 degrees, though depending on the type ofthe liquid crystal displays.

[Liquid Crystal Display]

The optical compensating film of the cellulose acetate film, and thepolarizing plate (circularly polarizing plate) that comprises thecellulose acetate film are favorable to liquid crystal displays. Theyapply to any of transmission, reflection or semi-transmission liquidcrystal displays, but are more favorable to reflection orsemi-transmission liquid crystal displays.

FIG. 8 is a graphic view showing the basic constitution of thereflection liquid crystal display of the invention.

As in FIG. 8, the reflection liquid crystal display comprises a lowersubstrate 11, a reflective electrode 12, a lower orientation film 13, aliquid crystal layer 14, an upper orientation film 15, a transparentelectrode 16, an upper substrate 17, a λ/4 plate 18 and a polarizingfilm 19 arrayed in that order from its bottom.

In this, the lower substrate 11 and the reflective electrode 12constitute a reflector. The lower orientation film 13 to the upperorientation film 15 constitute a liquid crystal cell. The λ/4 plate 18may be disposed in any site between the reflector and the polarizingfilm 19.

For displaying color images, the display shall have a color filter layer(not shown). The color filter layer is preferably between the reflectiveelectrode 12 and the lower orientation film 13, or between the upperorientation film 15 and the transparent electrode 16.

In the constitution of FIG. 8, a transparent electrode may be used inplace of the reflective electrode 12 and an additional reflector may bedisposed therein. For the reflector to be combined with the transparentelectrode, preferred is a metal plate. If the reflector is smooth-faced,regular reflective components only are reflected thereon and the fieldof view is often narrowed. Therefore, it is desirable that the surfaceof the reflector is roughened (as in Japanese Patent 275,620). In placeof roughening the surface of the smooth-faced reflector, alight-diffusive film may be disposed on one side of the polarizing film(on the side adjacent to the cell or on the outer side of the film).

The liquid crystal cell is not specifically defined. For it, any liquidcrystal mode is employable with no specific limitation, but preferredare TN (twisted nematic)-mode cells, STN (super twisted nematic)-modecells, HAN (hybrid aligned nematic)-mode cells, VA (verticallyaligned)-mode cells, ECB (electrically controlled birefringence)-modecells and OCB (optically compensatory bend)-mode cells.

Preferably, the twist angle in TN-mode liquid crystal cells fallsbetween 40 and 100°, more preferably between 50 and 90°, most preferablybetween 60 and 80°. The product (Δnd) of the refractivity anisotropy(Δn) of the liquid crystal layer and the thickness (d) thereofpreferably falls between 0.1 and 0.5 μm, more preferably between 0.2 and0.4 μm.

The twist angle in STN-mode liquid crystal cells preferably fallsbetween 180 and 360°, more preferably between 220 and 270°. The product(Δnd) of the refractivity anisotropy (Δn) of the liquid crystal layerand the thickness (d) thereof preferably falls between 0.3 and 1.2 μm,more preferably between 0.5 and 1.0 μm.

In HAN-mode liquid crystal cells, it is desirable that the liquidcrystal on one substrate is substantially vertically oriented and thepre-tilt angle of the liquid crystal on the other substrate is from 0 to45°. The product (Δnd) of the refractivity anisotropy (Δn) of the liquidcrystal layer and the thickness (d) thereof preferably falls between 0.1and 1.0 μm, more preferably between 0.3 and 0.8 μm. The substrate onwhich the liquid crystal is vertically oriented may be on the side ofthe reflector, or on the side of the transparent electrode.

In VA-mode liquid crystal cells, the rod liquid-crystalline moleculesare substantially vertically oriented with no voltage applied thereto.VA-mode liquid crystal cells include (1) those in the narrow sense ofthe word in which the rod liquid-crystalline molecules are substantiallyvertically oriented with no voltage applied thereto, but aresubstantially horizontally oriented with voltage applied thereto (as inJP-A176625/1990, JP-B69536/1995), and (2) those of multi-domain VA-modethat have the advantage of enlarged view angles. Concretely, the VA-modeliquid crystal cells (2) include MVA (SID97, described in Digest ofTech. Papers (preliminary), 28, (1997), 845; SID99 in Digest of Tech.Papers (preliminary), 30, (1999), 206, and JP-A258605/1999; SURVAILVAL(in Monthly Display, Vol. 6, No. 3 (1999), 14); PVA (in Asia Display 98,Proc. of the 18th Inter. Display Res. Conf. (preliminary) (1998), 383);Para-A (announced in LCD/PDP International '99); DDVA (SID98, in Digestof Tech. Papers (preliminary), 29, (1998), 845); EOC (SID98, in Digestof Tech. Papers (preliminary), 29, (1998), 313); PSHA (SID98, in Digestof Tech. Papers (preliminary), 29, (1998), 1081); RFFMA (in Asia Display98, Proc. of the 18th Inter. Display Res. Conf. (preliminary) (1998),337583); HMD (SID98, in Digest of Tech. Papers (preliminary), 29,(2998), 720). Apart from these, VA-mode liquid crystal cells furtherinclude (3) those in which the rod liquid-crystalline molecules aresubstantially vertically oriented with no voltage applied thereto, andare oriented in a mode of twisted multi-domain (n-ASM mode) with voltageapplied thereto (as in IWD '98, Proc. of the 5th Inter. Display Workshop(preliminary) (1998), 143).

In OCB-mode liquid crystal cells, the rod liquid-crystalline moleculesare substantially oppositely (symmetrically) oriented in the upper andlower parts of the liquid crystal cell. Having the constitution, thecells have a function of self-optical compensation. Their details aredescribed in U.S. Pat. Nos. 4,583,825, 5,410,422.

ECB-mode liquid crystal cells are characterized in that the liquidcrystal molecules therein are horizontally oriented, and their detailsare described in JP-A 203946/1993.

Reflection and semi-transmission liquid crystal displays are usable inany normally white mode that gives light display images under lowvoltage but gives dark display images under high voltage and in anynormally black mode that gives dark display images under low voltage butgives light display images under high voltage, but are more favorable tonormally white mode devices.

[Application to Touch Panel and Organic EL Displays]

The optical compensating film of the invention is applicable to touchpanels such as those in JP-A 127822/1993, 48913/2002.

The optical compensating film of the invention is also applicable toorganic EL displays such as those in JP-A 305729/1999, 307250/1999,267097/2000.

EXAMPLES

Examples of the invention are described below, to which, however, theinvention is not limited.

(1) Measurement of Haze:

The haze of each cellulose acetate film (optical compensating film)produced is measured with a haze meter (NDH1001-DP, from Nippon DenshokuKogyo). Concretely, five random points of one sample are measured, andtheir data are averaged to be the haze of the sample.

(2) Measurement of Water Content:

The water content of each sample is measured according to theCurl-Fisher method, which is as follows:

-   -   (i) The sample to be measured (0.9 m×4.5 cm, two sheets) is        weighed.    -   Water on the surfaces of wet samples is rapidly removed.        Immediately after its sampling, the sample is put into a ground        stopper bottle of glass, and is carried to a moisture meter.        Within 3 minutes after its sampling, the water content of the        sample is measured.    -   (ii) Using a moisture meter mentioned below, the water content        of the sample is measured.    -   Using an evaporator, Mitsubishi Chemical's VA-05 Model, water in        the sample was evaporated away at 150° C. and introduced into a        moisture meter.    -   Using a moisture meter, Curl-Fisher Moisture Meter (Mitsubishi        Chemical's CA-03 Model), the amount of water introduced        thereinto from the evaporator is measured.    -   (iii) Computation of water content:    -   The water content of the sample is computed as follows:        Water content (%)=0.1×(W/F)    -   in which W is the water content (μg) indicated by the moisture        meter and F is the weight (mg) of the sample.        (3) Water Film on Cellulose Acetate Film:

Filter paper is pressed against the cellulose acetate film just beforestretched, and the area of the filter paper having absorbed water fromthe film to change its color is measured. The area thus measured isdivided by the overall area of the filter paper, and it is representedin terms of percentage.

(4) Measurement of Retardation and NZ Factor:

The retardation and the NZ factor of each optical compensating film aremeasured as follows:

-   -   (i) Re450, Re550, Re590:    -   Using an automatic birefringence refractometer (KOBRA-21ADH/PR,        from Oji Test Instruments), the retardation value of the sample        film is measured with a ray of 450 nm, 550 nm or 590 nm applied        in the direction perpendicular to the film surface.    -   (ii) NZ factor ((nx−nz)/(nx−ny)):    -   Using an automatic birefringence refractometer (KOBRA-21ADH/PR,        from Oji Test Instruments), the retardation of the sample film        is measured with a ray of 550 nm applied in the direction        inclined by 40 degrees or −40 degrees from the direction        perpendicular to the film surface, and Re(0), Re(4) and Re(−40)        are obtained. From these, obtained are the refractive index, nx,        in the direction of the phase lag axis of the film, the        refractive index, ny, in the direction perpendicular to the        in-plane phase lag axis of the film, and the refractive index,        nz, in the direction of the thickness of the film. From the        thus-obtained data, the value of (nx−nz)/(nx−ny) is computed.        (5) Measurement of Degree of Acetyl Substitution:

According to the method described in Polymer Journal 17, 1065–1069(1985), the degree of acetyl substitution of each sample is measuredthrough ¹³C-NMR spectrometry.

(Formation of Cellulose Acetate Film 1)

A cellulose acetate solution having the composition mentioned below wasprepared.

Composition of Cellulose Acetate Solution Cellulose acetate (degree ofacetylation, 60.9%)   100 wt. pts. Triphenyl phosphate (plasticizer) 10.0 wt. pts. Biphenyldiphenyl phosphate (plasticizer)  5.0 wt. pts.Methylene chloride (first solvent) 565.6 wt. pts. Methanol (secondsolvent)  49.2 wt. pts. Retardation-controlling agent  1.97 wt. pts.Silica particles (20 nm)  0.05 wt. pts.

For the retardation-controlling agent, used was the following rodcompound:

The UV and visible (UV-vis) spectrum of the retardation-controllingagent was measured according to the method mentioned above. It gave anabsorption maximum at a wavelength (λmax) of 230 nm and its absorptioncoefficient (ε) was 16000.

The resulting dope was cast on a film-forming band, and dried at roomtemperature for 1 minute and then at 45° C. for 5 minutes. After dried,the amount of the solvent still remaining in the film was 30% by weight.The cellulose acetate film was peeled from the band, and dried at 100°C. for 10 minutes and then at 130° C. for 20 minutes. This is celluloseacetate film 1. The amount of the solvent still remaining in the film 1was 0.1% by weight, and the film thickness was 130 μm.

(Formation of Cellulose Acetate Film 2)

A cellulose acetate solution having the composition mentioned below wasprepared.

Composition of Cellulose Acetate Solution Cellulose acetate (degree ofacetylation, 60.9%)   100 wt. pts. Triphenyl phosphate (plasticizer) 10.0 wt. pts. Biphenyldiphenyl phosphate (plasticizer)  5.0 wt. pts.Methylene chloride (first solvent) 534.9 wt. pts. Methanol (secondsolvent)  79.9 wt. pts. Retardation-controlling agent  1.97 wt. pts.Silica particles (20 nm)  0.05 wt. pts.

The retardation-controlling agent used herein is the same as that usedin the cellulose acetate film 1.

The resulting dope was cast on a film-forming band, and dried at roomtemperature for 1 minute and then at 45° C. for 5 minutes. After dried,the amount of the solvent still remaining in the film was 30% by weight.The cellulose acetate film was peeled from the band, and dried at 100°C. for 10 minutes and then at 130° C. for 20 minutes. This is celluloseacetate film 2. The amount of the solvent still remaining in the film 2was 0.1% by weight, and the film thickness was 130 μm.

(Formation of Cellulose Acetate Film 3)

A cellulose acetate solution having the composition mentioned below wasprepared.

Composition of Cellulose Acetate Solution Cellulose acetate (degree ofacetylation, 60.9%)   100 wt. pts. Triphenyl phosphate (plasticizer) 10.0 wt. pts. Biphenyldiphenyl phosphate (plasticizer)  5.0 wt. pts.Methylene chloride (first solvent) 534.9 wt. pts. Methanol (secondsolvent)  79.9 wt. pts. Retardation-controlling agent  1.97 wt. pts.Silica particles (20 nm)  0.05 wt. pts.

For the retardation-controlling agent, used was the following tabularcompound.

The resulting dope was cast on a film-forming band, and dried at roomtemperature for 1 minute and then at 45° C. for 5 minutes. After dried,the amount of the solvent still remaining in the film was 30% by weight.The cellulose acetate film was peeled from the band, and dried at 100°C. for 10 minutes and then at 130° C. for 20 minutes. This is celluloseacetate film 3. The amount of the solvent still remaining in the film 3was 0.1% by weight, and the film thickness was 130 μm.

(Formation of Cellulose Acetate Film 4)

A cellulose acetate solution having the composition mentioned below wasprepared.

Composition of Cellulose Acetate Solution Cellulose triacetate (degreeof acetylation, 60.3%)   20 wt. pts. Methyl acetate   58 wt. pts.Acetone   5 wt. pts. Methanol   5 wt. pts. Ethanol   5 wt. pts. Butanol  5 wt. pts. Retardation-controlling agent  1.0 wt. pt. Plasticizer A(ditrimethylolpropane tetraacetate)  1.2 wt. pts. Plasticizer B(triphenyl phosphate)  1.2 wt. pts. UV absorbent a: 2,4-bis(n-octylthio-6-(4-hydroxy-3,5-di-tert-  0.2 wt. ptsbutylanilino)-1,3,5-triazine UV absorbent b:2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-  0.2 wt. pts.chlorobenzotriazole UV absorbent c:2-(2′-hydroxy-3′,5′-di-tert-amylphenyl)-5-  0.2 wt. ptschlorobenzotriazole C₁₂H₂₅OCH₂CH₂O—P(═O)—(OK)₂ (release agent) 0.02 wt.pts Citric acid (release agent) 0.02 wt. pts. Silica particles (particlesize, 20 nm; Mohs hardness, about 0.05 wt. pts. 7)

The retardation-controlling agent used herein is the same as that usedin the cellulose acetate film 1. In the cellulose acetate used herein,the 6-position is acetylated to a higher degree than the 2- and3-positions. In this, the degree of acetylation at the 6-, 2- and3-positions is 20.5%, 19.9% and 19.9%, respectively.

The constitutive components were dissolved according to a coolingdissolution method mentioned below. Concretely, the compounds weregradually added to the solvent with full stirring, and then left at roomtemperature (25° C.) for 3 hours for which the compounds well swelled.With gradually stirring it, the resulting swollen mixture was cooled to−30° C. at a rate of −8° C./min, and then to −70° C. After 6 hours, thiswas then heated at a rate of +8° C./min. In the stage when this formed asol in some degree, stirring it was started. This was further heated upto 50° C. to obtain a dope.

The resulting dope was cast on a film-forming band, and dried at roomtemperature for 1 minute and then at 45° C. for 5 minutes. After dried,the amount of the solvent still remaining in the film was 30% by weight.The cellulose acetate film was peeled from the band, and dried at 100°C. for 10 minutes and then at 130° C. for 20 minutes. This is celluloseacetate film 4. The amount of the solvent still remaining in the film 4was 0.1% by weight, and the film thickness was 130 μm.

(Preliminary Experiment 1 for Film to Absorb Water)

The cellulose acetate film 1 formed in the above was dipped in a waterthermostat at 80° C., and it was analyzed in point of the relationbetween the dipping time and the water content of the film. Dipped inwater for 0 minute, 1 minute, 2 minutes, 4 minutes, 8 minutes and 20minutes, the water content of the film was 1.89% by weight, 3.78% byweight, 4.21% by weight, 4.53% by weight, 4.79% by weight and 4.83% byweight, respectively. The other cellulose acetate films 2 to 4 were alsoanalyzed in the same manner as above in point of the dipping time andthe water content thereof. The results of these films were almost thesame as those of the film 1.

(Preliminary Experiment 2 for Film to Absorb Water)

The cellulose acetate film 1 formed in the above was put in ahigh-humidity thermostat at 80° C. and 95% RH, and it was analyzed inpoint of the relation between the moisturizing time and the watercontent of the film. Moisturized for 0 minute, 1 minute, 2 minutes, 4minutes, 8 minutes and 20 minutes, the water content of the film was1.89% by weight, 2.91% by weight, 3.25% by weight, 3.54% by weight,3.57% by weight and 3.56% by weight, respectively. The other celluloseacetate films 2 to 4 were also analyzed in the same manner as above inpoint of the moisturizing time and the water content thereof. Theresults of these films were almost the same as those of the film 1.

Example 1

(Formation of Optical Compensating Film 1)

The cellulose acetate film 1 formed in the above was dipped in a waterthermostat at 80° C. for 5 minutes. Thus dipped, the film absorbed waterto have a water content of 4.63% by weight. Then, this was put into anair thermostat at 90° C., and then immediately stretched by 42.5%. Thiswas stretched in a clip-to-clip stretching method, in which the aspectratio (L/W) was 0.8 and the stretching time was 9 seconds. Immediatelyafter stretched, the water content of the film was 4.7% by weight. Next,this was dried in a thermostat at 80° C. for 3 minutes, and thenconditioned at 25° C. and 60% RH for at least 2 hours. The opticalproperties of the film were measured, and the data obtained are given inTable 1. After stretched, the thickness of the film was 115 μm.

Example 2

(Formation of Optical Compensating Film 2)

The cellulose acetate film 1 formed in the above was dipped in a waterthermostat at 80° C. for 5 minutes. Thus dipped, the film absorbed waterto have a water content of 4.63% by weight. Then, this was put into ahigh-humidity thermostat at 70° C. and 95% RH, and then immediatelystretched by 35%. This was stretched in a clip-to-clip stretchingmethod, in which the stretch aspect ratio (L/W) was 0.8 and thestretching time was 7 seconds. Immediately after stretched, the watercontent of the film was 4.8% by weight. After taken out, the film wasdried in a thermostat at 80° C. for 3 minutes, and then conditioned at25° C. and 60% RH for at least 2 hours. The optical properties of thefilm were measured, and the data obtained are given in Table 1. Afterstretched, the thickness of the film was 117 μm.

Example 3

(Formation of Optical Compensating Film 3)

The cellulose acetate film 1 formed in the above was dipped in a waterthermostat at 80° C. for 5 minutes. Thus dipped, the film absorbed waterto have a water content of 4.63% by weight. Then, this was put into ahigh-humidity thermostat at 70° C. and 95% RH, and then immediatelystretched by 42.5%. This was stretched in a clip-to-clip stretchingmethod, in which the stretch aspect ratio (L/W) was 1.0 and thestretching time was 9 seconds. Immediately after stretched, the watercontent of the film was 4.8% by weight. After taken out, the film wasdried in a thermostat at 80° C. for 3 minutes, and then conditioned at25° C. and 60% RH for at least 2 hours. The optical properties of thefilm were measured, and the data obtained are given in Table 1. Afterstretched, the thickness of the film was 115 μm.

Example 4

(Formation of Optical Compensating Film 4)

The cellulose acetate film 1 formed in the above was put in ahigh-humidity thermostat at 80° C. and 95% RH for 5 minutes. Thus puttherein, the film absorbed water to have a water content of 3.55% byweight, and it was stretched by 45.0%. This was stretched in aclip-to-clip stretching method, in which the stretch aspect ratio (L/W)was 1.0 and the stretching time was 9 seconds. Immediately afterstretched, the water content of the film was 4.8% by weight. After takenout, the film was dried in a thermostat at 80° C. for 3 minutes, andthen conditioned at 25° C. and 60% RH for at least 2 hours. The opticalproperties of the film were measured, and the data obtained are given inTable 1. After stretched, the thickness of the film was 115 μm.

Example 5

(Formation of Optical Compensating Film 5)

The cellulose acetate film 1 formed in the above was put in ahigh-humidity thermostat at 80° C. and 95% RH for 5 minutes. Thus puttherein, the film absorbed water to have a water content of 3.55% byweight. Then, this was stretched by 45.0% while exposed to high-pressurewater vapor at 120° C. for 2 seconds. This was stretched in aclip-to-clip stretching method, in which the stretch aspect ratio (L/W)was 1.0 and the stretching time was 9 seconds. Immediately afterstretched, the water content of the film was 3.7% by weight. After takenout, the film was dried in a thermostat at 80° C. for 3 minutes, andthen conditioned at 25° C. and 60% RH for at least 2 hours. The opticalproperties of the film were measured, and the data obtained are given inTable 1. After stretched, the thickness of the film was 115 μm.

Comparative Example 1

(Formation of Optical Compensating Film 6)

The cellulose acetate film 1 formed in the above was put in a thermostatat 130° C. for 5 minutes. Thus put therein, the film had a water contentof 0.4% by weight, and then it was stretched by 37%. This was stretchedin a clip-to-clip stretching method, in which the stretch aspect ratio(L/W) was 3.3. Then, the film was conditioned at 25° C. and 60% RH forat least 2 hours. The optical properties of the film were measured, andthe data obtained are given in Table 1. After stretched, the thicknessof the film was 115 μm.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Comp. Ex. 1Draw Ratio 42.5% 35.0% 42.5% 45.0% 45.0% 37.0% Re450 [nm] 128 106 129121 123 124 Re550 [nm] 142 118 143 134 137 138 Re590 [nm] 145 120 146137 140 141 (nx − nz)/ 1.62 1.85 1.66 1.76 1.60 1.32 (nx − ny) (NZfactor) Haze 0.3 0.4 2.0 0.4 0.5 0.4

The other cellulose acetate films 2 to 4 formed in the above wereprocessed in the same manner as in Examples 1 to 5 into opticalcompensating films, all of which had almost the same data as in Table 1.

Example 6

(Fabrication of Circularly Polarizing Plates)

A PVA film was dipped in an aqueous solution of iodine (2.0 g/liter) andpotassium iodide (4.0 g/liter) at 25° C. for 240 seconds, and then in anaqueous solution of boric acid (10 g/liter) at 25° C. for 60 seconds.Then, this was introduced into a tenter-type stretching machine as inFIG. 7, and stretched 5.3-fold therein. The tenter in the machine is sodesigned that it bends in the machine direction as in FIG. 7, and afterthe bent zone, its width is kept constant. After dried in an atmosphereat 80° C., the stretched film was taken out of the tenter. Thefilm-traveling speed difference between the tenter clips on both sidesof the tenter was smaller than 0.05%, and the angle of the centerline ofthe film just having been introduced into the tenter to the centerlineof the stretched film to be fed to the next stage was 46°. In this step,|L1−L2| was 0.7 m and W was 0.7 m, or that is, |L1−L2|=W. At the tenteroutlet, the tilt angle of the substantial stretched direction, Ax−Cx, ofthe film to the centerline 22 of the stretched film to be fed to thenext stage was 45°. At the tenter outlet, neither film shrinkage norfilm deformation was found. Using an adhesive of aqueous 3% PVA(Kuraray's PVA-117H) solution, a saponified film of Fuji Photo Film'sFujitac (cellulose triacetate having a retardation value of 3.0 nm), andthe optical compensating film 4 of Example 4 that had been saponified onits one surface were laminated with the polarizing film prepared herein,in a mode of roll-to-roll lamination where the adhesive-coated surfaceof each film was kept in contact with the polarizing film. The processgave a circularly polarizing plate. The same process, in which, however,the optical compensating film 5 of Example 5 that had been saponified inthe same manner on its one surface was used in place of the opticalcompensating film 4, also gave a circularly polarizing plate.

The optical properties of the circularly polarizing plates thusfabricated herein were measured. Both the circularly polarizing platesattained almost complete circular polarization in a broad wavelengthrange (450 to 590 nm).

Example 7

(Fabrication of TN-Mode Reflection Liquid Crystal Displays)

A glass substrate with an ITO transparent electrode mounted thereon, anda glass substrate with a surface-roughened, reflective aluminiumelectrode mounted thereon were prepared. An orientation film ofpolyimide (SE-7992 from Nissan Chemical) was formed on the electrode ofeach of the two glass substrates, and rubbed. Via a 1.7 μm-spacer puttherebetween, the two substrates were stacked with their orientationfilms facing each other. In stacking them, the two substrates were socontrolled that the rubbing directions of the two orientation filmsthereon cross at an angle of 110°. A liquid crystal (MLC-6252 fromMerck) was introduced into the space between the substrates to form aliquid crystal layer therebetween. The process gave a TN-mode liquidcrystal cell having a twist angle of 70° and a value Δnd of 269 nm.

Any of the two circularly polarizing plates that had been fabricated inExample 6 (each laminated with a protective film of which the surfacehad been AR-processed) was stuck to the ITO transparent electrode-havingglass substrate on its side opposite to the side of the electrodethereof, in such a manner that the cellulose acetate film of thepolarizing plate faces the substrate.

A rectangular wave voltage of 1 kHz was applied to the thus-fabricated,reflection liquid crystal display. The display was visually checked at1.5 V for white expression and 4.5V for black expression. It wasconfirmed that both the white expression and the black expression wereneutral gray with no other color.

Next, using a contrast meter (EZ Contrast 160D from Eldim), the contrastratio of the reflection brightness of the display was measured. Thecontrast ratio in front of the display was 25, and the field of view(view angle) to give a contrast ratio of 10 was at least 120° in thevertical direction and at least 120° in the horizontal direction. In adurability test at 60° C. and 90% RH for 500 hours, the display was goodwith no problem of expression.

Example 8

(Fabrication of STN-Mode Reflection Liquid Crystal Displays)

A glass substrate with an ITO transparent electrode mounted thereon, anda glass substrate with a smooth reflective aluminium electrode mountedthereon were prepared. An orientation film of polyimide (SE-150 fromNissan Chemical) was formed on the electrode of each of the two glasssubstrates, and rubbed. Via a 6.0 μm-spacer put therebetween, the twosubstrates were stacked with their orientation films facing each other.In stacking them, the two substrates were so controlled that the rubbingdirections of the two orientation films thereon cross at an angle of60°. A liquid crystal (ZLI-2977 from Merck) was introduced into thespace between the substrates to form a liquid crystal layertherebetween. The process gave an STN-mode liquid crystal cell having atwist angle of 240° and a value Δnd of 791 nm.

Using an adhesive, an internal diffusive sheet (IDS from Dai-NipponPrinting) and any of the two circularly polarizing plates that had beenfabricated in Example 6 were stuck in that order to the ITO transparentelectrode-having glass substrate on its side opposite to the side of theelectrode thereof, in such a manner that the polarizing plate is theoutermost layer.

A rectangular wave voltage of 55 Hz was applied to the thus-fabricated,reflection liquid crystal display. The display was visually checked at2.0 V for black expression and at 2.5 V for white expression. It wasconfirmed that both the white expression and the black expression wereneutral gray with no other color.

Next, using a contrast meter (EZ Contrast 160D from Eldim), the contrastratio of the reflection brightness of the display was measured. Thecontrast ratio in front of the display was 8, and the field of view(view angle) to give a contrast ratio of 3 was 90° in the verticaldirection and 105° in the horizontal direction.

Example 9

[VA-mode Liquid Crystal Displays]

FIG. 9 is a cross-sectional view showing the basic constitution of aVA-mode liquid crystal display. As in FIG. 9, the VA-mode liquid crystaldisplay illustrated comprises a lower glass substrate 41, an insulationfilm 39, a thin-film transistor 38, a reflector 36, a lower orientationfilm 35, a liquid crystal 40, an upper orientation film 34, an ITOtransparent electrode 33, an overcoat layer 32, a color filter 31 and anupper glass substrate 30 arrayed in that order from its bottom.

A glass substrate 30 with an ITO transparent electrode 33 mountedthereon, and a glass substrate 41 with a surface-roughened, reflectivealuminium electrode 35 to 39 mounted thereon were prepared. Verticalorientation films (RN783 from Nissan Chemical) were prepared for theupper orientation film 34 and the lower orientation film 35, and theywere rubbed. Via a 1.7 μm-spacer put therebetween, the two substrateswere stacked with their orientation films facing each other. In stackingthem, the two substrates were so controlled that the rubbing directionsof the two orientation films thereon cross at an angle of 110°. A liquidcrystal having Δn=0.08 and Δε=−4 (from Merck) was introduced throughvacuum injection into the space between the substrates to form a liquidcrystal layer (40) therebetween. The process gave a VA-mode liquidcrystal cell having a twist angle of 45° and a value Δnd of 135 nm.

Using an adhesive, the optical compensating film formed in Example 4,and a commercially-available polarizing plate (HLC2-5618HCS fromSanritz) were stuck in that order to the ITO transparentelectrode-having glass substrate on its side opposite to the side of theelectrode thereof. In sticking the optical compensating film and thepolarizing plate to the substrate, they were so controlled that theabsorption axis of the polarizing plate crosses the phase lag axis ofthe optical compensating film at an angle of 45 degrees. The devicesthus fabricated herein to have the optical compensating film 4 ofExample 4 all had a broad field of view, concretely having a view angleof at least 160 degrees in the vertical direction and a view angle of atleast 160 degrees in the horizontal direction. In place of the opticalcompensating film 4 of Example 4, the optical compensating film 5 ofExample 5 was used to fabricate the devices of the same constitution asherein. Thus fabricated, all the devices also had a broad field of view,concretely having a view angle of at least 160 degrees in the verticaldirection and a view angle of at least 160 degrees in the horizontaldirection. However, when the optical compensating film 6 formed inComparative Example 1 was used, the view angle of the devices was notlarger than 140 degrees in both the vertical direction and thehorizontal direction.

A VA-mode liquid crystal cell was formed in the same manner as herein,and the circularly polarizing plate formed in Example 6 was stuck to theITO transparent electrode-having glass substrate on its side opposite tothe side of the electrode thereof, using an adhesive. Thus fabricated,the device also had a broad field of view, concretely having a viewangle of at least 160 degrees in the vertical direction and a view angleof at least 160 degrees in the horizontal direction.

As demonstrated herein, the angle dependency of the birefringence (Δn)of liquid crystal cells varies depending on the liquid crystal panelscombined with the cells, and the view angle characteristic of liquidcrystal displays could not be optimized by merely controlling Re. It isunderstood from the data in this example that the matter of importancefor the view angle characteristic optimization in fabricating liquidcrystal displays is to control the NZ factor of the optical compensatingfilm used, not varying Re thereof.

Example 10

(ECB-Mode Liquid Crystal Displays)

According to the process of Example 1 in JP-A 316378/1999, circularlypolarizing plates were fabricated in which, however, the opticalcompensating films 4, 5 and 6 that had been formed in Examples 4 and 5and Comparative Example 1, respectively, were used for the secondtransparent support. When the optical compensating film was stuck to thepolarizing film, they were so controlled that the absorption axis of thepolarizing film crosses the phase lag axis of the optical compensatingfilm at an angle of 45 degree. Using the circularly polarizing platesthus fabricated herein, ECB-mode liquid crystal displays wereconstructed according to the process of Example 6 in JP-A 316378/1999.The devices comprising the optical compensating film of the inventionall had a broad field of view, concretely having a view angle of atleast 120 degrees in the vertical direction and a view angle of at least115 degrees in the horizontal direction. However, the devices comprisingthe optical compensating film of Example 1 were not so good, concretelyhaving a view angle of not larger than 100 degrees in both the verticaldirection and the horizontal direction.

Example 11

(Organic EL Device-Having Displays)

According to JP-A 267097/2000, a display having a constitution ofprotective tack (provided with an antireflection layer on its outermostsurface)/polarizing film/optical compensating film/organic ELdevice/reflective electrode arrayed in that order from the side ofviewers was fabricated, in which the optical compensating film 4 or 5formed in Examples 4 or 5 was used. In this, the polarizing film and theoptical compensating film were so arrayed that the transmission axis ofthe former crosses the phase lag axis of the latter at an angle of 45°.Thus fabricated, the display was visually checked for its colorexpression. It was confirmed that the black expression in the display iscolored little, and therefore the contrast of the display is high andthe visibility thereof is good.

Example 12

(Packaging in Semi-Transmission Devices)

Cybershot (from Sony) was modified as follows: The polarizing plate, theλ/2 plate and the λ/4 plate in the upper part of the liquid crystal cellin the liquid crystal display unit were peeled off. Using an adhesive,the optical compensating film 4 or 5 (λ/4 plate) formed in Example 4 or5, and a commercially-available polarizing plate (HLC2-5618HCS fromSanritz) were laminated in that order on the glass substrate. Inlaminating the optical compensating film and the polarizing film on thesubstrate, they were so controlled that the absorption axis of thepolarizing film crosses the phase lag axis of the optical compensatingfilm at an angle of 45 degrees. The devices comprising the opticalcompensating film 4 or 5 of Examples 4 or 5 all had a broad field ofview, concretely having a view angle of at least 120 degrees in thevertical direction and a view angle of at least 115 degrees in thehorizontal direction.

Comparative Example 2

In the same manner as in Example 12, the device was modified, for which,however, used was the optical compensating film 6 formed in ComparativeExample 1. The thus-modified device was inferior to those of Example 12in point of the field of view. Concretely, its view angle was 100degrees in the vertical direction and 100 degrees in the horizontaldirection.

Example 13

(Packaging in Reflection Liquid Crystal Displays)

A tough panel-having reflection liquid crystal display (Sharp's Zaurus)was modified as follows: The polarizing plate and the opticalcompensating film in the structure of touch panel/polarizingplate/optical compensating film/liquid crystal cell of the display werepeeled off and replaced with the optical compensating film 4 or 5 ofExample 4 or 5 and a commercially-available polarizing plate(HLC2-5618HCS from Sanritz). For this, the polarizing plate and theoptical compensating film were so controlled that the absorption axis ofthe former crosses the phase lag axis of the latter at an angle of 45degrees. This is for maximizing the contrast of the modified device.Thus modified, the liquid crystal displays having the opticalcompensating film 4 or 5 of Example 4 or 5 had a broad field of view,concretely having a view angle of at least 120 degrees in the verticaldirection and a view of angle of at least 115 degrees in the horizontaldirection.

Comparative Example 3

In the same manner as in Example 13, the device was modified, for which,however, used was the optical compensating film 6 formed in ComparativeExample 1. The thus-modified device was inferior to those of Example 13in point of the field of view. Concretely, its view angle was 100degrees in the vertical direction and 100 degrees in the horizontaldirection.

Example 14

1. Formation of Optical Compensating Films (Stretched Cellulose AcetateFilms):

(1) Composition:

A cellulose acetate dope (high-concentration solution) having thecomposition mentioned below was prepared. In this, the rod compound orthe tabular compound mentioned above was used for theretardation-controlling agent (aromatic compound having at least twoaromatic rings).

(α) Methylene Chloride (MC)-Based Composition:

Cellulose acetate (its degree of acetylation is in Table   100 wt. pts.2) Triphenyl phosphate   10 wt. pts. Biphenyldiphenyl phosphate    5 wt.pts. Methylene chloride 565.6 wt. pts. Methanol  49.2 wt. pts.Retardation-controlling agent (Re-controlling agent) as in Table 2Silica particles (particle size, 20 nm)  0.05 wt. pts.(β) Methyl Acetate (MA)-Based Composition:

Cellulose acetate (its degree of acetylation is in Table   118 wt. pts.2) Triphenyl phosphate  9.19 wt. pts. Biphenyldiphenyl phosphate  4.60wt. pts. Tribenzylamine  2.36 wt. pts. Methyl acetate   530 wt. pts.Ethanol  99.4 wt. pts Butanol  33.1 wt. pts. Methylene chloride 565.6wt. pts. Retardation-controlling agent (Re-controlling agent) as inTable 2 Silica particles (particle size, 20 nm)  0.05 wt. pts.(2) Dissolution:

The MC-based composition was dissolved in a room-temperature dissolutionmethod; and the MA-based composition was in a cooling dissolutionmethod. The two gave two different dopes.

(a) Room-Temperature Dissolution Method:

With well stirring, the above-mentioned compounds were gradually addedto the solvent, and left at room temperature (25° C.) for 3 hours forwhich they well swelled. The resulting swollen mixture was put into amixer tank equipped with a reflex condenser, and dissolved with stirringat 50° C.

(b) Cooling Dissolution Method:

With well stirring, the above-mentioned compounds were gradually addedto the solvent, and left at room temperature (25° C.) for 3 hours forwhich they well swelled. With gradually stirring, the resulting swollenmixture was cooled to −30° C. at a rate of −8° C./min, and then to −70°C. After 6 hours, this was then heated at a rate of +8° C./min. In thestage when this formed a sol in some degree, stirring it was started.This was further heated up to 50° C. to obtain a dope.

(3) Film Formation:

The dope was formed into a film according to any of the following twomodes, as in Table 2.

(α) Single-Layer Film Formation:

The solution (dope) obtained in the method as above was filtered throughfilter paper (Azumi Filter's No. 244) and through flannel cloth, thenfed into a pressure die via a metering gear pump. Using a castingmachine with a band having an effective length of 6 m, this was cast onthe band so that its final thickness after dried and stretched could beas in Table 2. The band temperature was 0° C. Thus cast, the film wasexposed to air for 2 seconds to dry it. When the volatile content of thefilm reached 50% by weight, the film was peeled off from the band. Then,this was stepwise dried at 100° C. for 3 minutes, at 130° C. for 5minutes and at 160° C. for 5 minutes, not fixed but allowed to freelyshrink. Thus dried, the solvent remaining in the film was reduced to atmost 1%.

(β) Multi-Layer Film Formation:

Using a three-layer co-casting die unit, the dope having the compositionas above was cast through the center die on a metal support while, atthe same time, the dope having been diluted to have an increased solventcontent of 10% by weight was through the two outer dies thereon to. Thusco-cast, the multi-layer film was peeled off from the support and dried.This is a three-layered cellulose acetate film laminate of the invention(thickness of the inner layer/thickness of each surface layer=8/1). Thiswas stepwise dried at 70° C. for 3 minutes and then at 130° C. for 5minutes on a glass sheet, and the film was peeled off from the glasssheet. Then, this was further dried at 160° C. for 30 minutes to removethe solvent to obtain a dry cellulose acetate film.

Next, the film was trimmed by 15 cm at both edges, and its edges of 1 cmwide were knurled to a height of 50 μm. The non-stretched celluloseacetate film thus obtained had a width of 1.5 m and a length of 3000 m.The trimmed cellulose acetate film waste was ground, and then mixed withnon-used cellulose acetate. In that manner, this is recycled. (Theamount of the recycled cellulose acetate is 30% by weight of allcellulose acetate used herein.)

(4) Stretching:

Using at least two pairs of nip rolls as in the apparatus of any of FIG.1 to FIG. 6, the cellulose acetate film was stretched under thecondition indicated in Table 2. Concretely, the film was passed betweenthe nip rolls while the rotation speed of the nip rolls at the outlet ofthe stretching unit is made to differ from that of the nip rolls at theinlet thereof. Thus stretched, this is an optical compensating film(phase-shift film) of the invention.

For making it absorb water before stretching, the film was dipped inwater or exposed to water vapor. For the latter, the film was dipped inwater at 90° C.; and for the latter, the film was exposed to water vaporat 120° C. Thus having absorbed water, the water content of the film isas in Table 2.

In case where two pairs of nip rolls were used, the film was stretchedin one stage; and in case where three or more pairs of nip rolls wereused, the film was stretched in multiple stages. In the multi-stagestretching process, the paired nip rolls were arrayed in tandem, and thedraw ratios in all the stretching stages were multiplied. The resultingproduct is shown as the draw ratio in Table 2. In stretching the filmthrough them, all the nip rolls were so controlled that the film couldbe uniformly stretched through them in every stretching stage.

The temperature difference in stretching the film is indicated by theequation mentioned below. In multi-stage stretching, the temperaturecondition was the same in every stage.

MD (Machine Direction):Stretching temperature difference=(temperature in the center pointbetween the outlet-side nip rolls and the inlet-side niprolls)−(temperature just after the inlet-side nip rolls)TD (Transverse Direction):Stretching temperature difference=(mean temperature at both edges inTD)−(temperature in the center part in TD)

All the nip rolls used had a diameter of 30 cm. One of the paired niprolls was covered with a 10 mm-thick rubber.

After stretched, every film was dried for 3 minutes, while conveyedunder a tension of 10 kg/m at 80° C. Then, its both edges were knurled,and the stretched film was wound up.

After stretched, every film had a width of 1.2 m.

TABLE 2 Dope Cellulose Optical Acetate Number of Moisturization beforestertching Compensating degree of Re Improver Layers of Water film Typeacetylation weight* % Type Film Method Content % Water Film % Samples ofthe Invention 11 MC 60.9 1.97 Rod 1 exposure to 4.5 3 water vapor 12 ″ ″″ ″ ″ exposure to ″ ″ water vapor 13 ″ ″ ″ ″ ″ exposure to ″ ″ watervapor 14 ″ ″ ″ ″ ″ exposure to ″ 33 water vapor 15 ″ ″ ″ ″ ″ exposure to″ 3 water vapor 16 ″ ″ ″ ″ ″ exposure to ″ ″ water vapor 17 ″ ″ ″ ″ ″exposure to 2 ″ water vapor 18 ″ ″ ″ ″ ″ exposure to 10 ″ water vapor 19″ ″ 10 ″ ″ exposure to 4.5 ″ water vapor 20 ″ ″ 0.01 ″ ″ exposure to ″ ″water vapor 21 MA 57 5 Tabular 3 dipping in water 7 26 22 MC 62.5 0.8 ″1 exposure to 3 15 water vapor Comparative MC 60.9 1.97 Rod 1 exposureto 1 3 Sample water vapor 23 Stretching Step Stretching TemperatureDifference Stretching after stretched Optical in Difference AspectAtmosphere Paired Water Compensating average TD in MD Ratio Timehumidity Nip Content Thickness film ° C. ° C. ° C. Draw Ratio (L/W)(sec) %** Rolls % μm Samples of the Invention 11 80 4 4 1.45 1.1 9exposure to 95 2 4.1 115 water vapor 12 ″ 0 0 4 ″ ″ exposure to ″ ″ ″ ″water vapor 13 ″ 25 25 0 ″ ″ exposure to ″ ″ ″ ″ water vapor 14 ″ ″ ″ 25″ ″ exposure to ″ ″ ″ ″ water vapor 15 ″ ″ ″ ″ 0.5 ″ exposure to ″ ″ ″ ″water vapor 16 ″ ″ ″ ″ 2.5 ″ exposure to ″ ″ ″ ″ water vapor 17 150 ″ ″″ 1.1 ″ exposure to ″ ″ 1 ″ water vapor 18 70 ″ ″ ″ ″ ″ exposure to ″ ″9 ″ water vapor 19 80 ″ ″ ″ ″ ″ exposure to ″ ″ 4.1 ″ water vapor 20 ″ ″″ ″ ″ ″ exposure to ″ ″ 4.1 ″ water vapor 21 70 2 18 1.2 0.8 2 exposureto 80 2 6 245 water vapor 22 100 18 2 1.9 1.5 29 dipping in — 4 2 45water Comparative 80 4 4 1.1 1.1 9 exposure to 95 2 4.1 115 Sample watervapor 23 *relative to cellulose acetate **relative humidity(5) Evaluation of Optical Compensating Films (Phase-Shift Films):

The optical properties of the thus-obtained optical compensating films11 to 23 are shown in Table 3. Re550 was measured at the center part inthe transverse direction and at the two edges (of which the data wereaveraged) of each film. The others except it were measured all at thecenter part of each film.

In Table 3, also shown are the data of the contrast ratio and the viewangle measured with the TN-mode, STN-mode and HAN-mode liquid crystaldisplays fabricated hereinunder.

TABLE 3 Reflection Liquid Crystal Display TN-mode Re (nx − ny)/ viewangle Optical Re550 (nz − ny) vertical horizontal Compensating centeredge Re450/ Re650/ (NZ contrast direction direction Film mm mm Re550Re550 factor) Haze % ratio degrees degrees (Samples of the Invention) 11138 138 0.83 1.15 1.6 0.3 25 125 125 12 ″ 155 ″ ″ ″ ″ 22 115 115 13 ″115 ″ ″ ″ ″ 23 115 115 14 ″ 150 ″ ″ ″ 1.9 24 115 120 15 270 330 0.651.30 1.2 1.1 21 110 110 16 95 105 0.94 1.06 2.5 0.7 21 110 110 17 200240 0.75 1.24 1.3 0.5 21 115 110 18 110 120 0.88 1.09 1.9 0.7 21 110 11519 83 86 0.98 1.02 1.1 0.2 20 105 110 20 310 320 0.53 1.34 2.9 1.5 20105 105 21 155 170 0.79 1.20 1.7 0.4 22 120 115 22 120 125 0.71 1.20 2.22.2 20 110 110 (Comparative Sample) 23 270 360 0.4 1.45 0.8 2.4 15 90 90Reflection Liquid Crystal Display STN-mode HAN-mode view angle viewangle Optical vertical horizontal vertical horizontal Compensatingcontrast direction direction contrast direction direction Film ratiodegrees degrees ratio degrees degrees (Samples of the Invention) 11 8 90105 8 125 125 12 7 80 90 7 110 110 13 7 80 90 7 110 105 14 7 85 90 7 110110 15 6 80 85 6 100 105 16 6 80 85 6 105 100 17 6 85 80 6 100 105 18 685 80 6 100 105 19 5.5 80 80 5.5 100 100 20 5.5 80 80 5.5 100 100 21 785 95 7 115 110 22 5 80 80 5 100 100 (Comparative Sample) 23 . 70 70 490 902. Fabrication of Circularly Polarizing Plates:(1) Formation of Polarizing Film:

PVA having a mean degree of polymerization of 4000 and a degree ofsaponification of 99.8 mol % was dissolved in water to prepare anaqueous 4.0% PVA solution. The solution was cast on a band, dried,peeled off from the band, stretched in dry in the machine direction,directly dipped in an aqueous solution of iodine (0.5 g/liter) andpotassium iodide (50 g/liter) at 30° C. for 1 minute and then in anaqueous solution of boric acid (100 g/liter) and potassium iodide (60g/liter) at 70° C. for 5 minutes, rinsed in water at 20° C. for 10minutes, and then dried at 80° C. for 5 minutes. The process gave along-continuous polarizing film (CHM-1). Its width was 1290 mm and itsthickness was 20 μm.

(2) Saponification of Optical Compensating Film:

Using a bar #3, a saponifying agent mentioned below was applied to onesurface of each of the optical compensating films 11 to 23 at 60° C.After 30 seconds, the films were rinsed in water and dried.

-   -   Saponifying agent: KOH was dissolved in iso-propanol/propylene        glycol/water (70/15/15, by volume) to prepare a 1.5 N KOH        solution. This is the saponifying agent used herein.        (3) Fabrication of Circularly Polarizing Plates:

Any of the optical compensating films (phase-shift films) 11 to 23, thepolarizing film formed in the above, and a commercially-availablecellulose acetate film (Fujitac from Fuji Photo Film) were laminated inthat order through roll-to-roll lamination to fabricate circularlypolarizing plates. In these, the saponified surface of the phase-shiftfilm was made to face the underlying polarizing film. The samples cutout of the two edges of each stretched film, of which the opticalproperties vary most significantly, were used herein.

The optical properties of the thus-fabricated circularly polarizingplates were measured. Those comprising the optical compensating film ofthe invention all attained almost complete circular polarization in abroad wavelength range (450 to 590 nm).

3. Fabrication of TN-Mode Reflection Liquid Crystal Displays:

A glass substrate with an ITO transparent electrode mounted thereon, anda glass substrate with a surface-roughened, reflective aluminiumelectrode mounted thereon were prepared. An orientation film ofpolyimide (SE-7992 from Nissan Chemical) was formed on the electrode ofeach of the two glass substrates, and rubbed. Via a 3.4 μm-spacer puttherebetween, the two substrates were stacked with their orientationfilms facing each other. In stacking them, the two substrates were socontrolled that the rubbing directions of the two orientation filmsthereon cross at an angle of 110°. A liquid crystal (MLC-6252 fromMerck) was introduced into the space between the substrates to form aliquid crystal layer therebetween. The process gave a TN-mode liquidcrystal cell (diagonal length; 12 inches) having a twist angle of 70°and a value Δnd of 269 nm.

Any of the circularly polarizing plates that had been fabricated in theabove (each laminated with a protective film of which the surface hadbeen AR-processed) was stuck to the ITO transparent electrode-havingglass substrate on its side opposite to the side of the electrodethereof, in such a manner that the cellulose acetate film of thepolarizing plate faces the substrate.

A rectangular wave voltage of 1 kHz was applied to the thus-fabricated,reflection liquid crystal display. The display was visually checked at1.5 V for white expression and 4.5 V for black expression. It wasconfirmed that both the white expression and the black expression wereneutral gray with no other color.

Next, using a contrast meter (EZ Contrast 160D from Eldim), the contrastratio of the reflection brightness of the display was measured. The dataof the contrast ratio in front of the display and the field of view(view angle) to give a contrast ratio of 3 are shown in Table 2. Thoughthe edges of the stretched film, of which the optical properties varymost significantly, were used for the optical compensating films hereinand though the displays fabricated all had a relatively large pictureplane (diagonal length, 12 inches), good pictures were seen in theentire region of the large picture plane.

4. Fabrication of STN-Mode Reflection Liquid Crystal Displays:

A glass substrate with an ITO transparent electrode mounted thereon, anda glass substrate with a smooth reflective aluminium electrode mountedthereon were prepared. An orientation film of polyimide (SE-150 fromNissan Chemical) was formed on the electrode of each of the two glasssubstrates, and rubbed. Via a 6.0 μm-spacer put therebetween, the twosubstrates were stacked with their orientation films facing each other.In stacking them, the two substrates were so controlled that the rubbingdirections of the two orientation films thereon cross at an angle of60°. A liquid crystal (ZLI-2977 from Merck) was introduced into thespace between the substrates to form a liquid crystal layertherebetween. The process gave an STN-mode liquid crystal cell (diagonallength, 12 inches) having a twist angle of 240° and a value Δnd of 791nm.

Using an adhesive, an internal diffusive sheet (IDS from Dai-NipponPrinting) and the circularly polarizing plate that had been fabricatedin the above were stuck in that order to the ITO transparentelectrode-having glass substrate on its side opposite to the side of theelectrode thereof, in such a manner that the polarizing plate is theoutermost layer.

A rectangular wave voltage of 55 Hz was applied to the thus-fabricated,reflection liquid crystal display. The display was visually checked at2.0 V for black expression and at 2.5 V for white expression. It wasconfirmed that both the white expression and the black expression wereneutral gray with no other color.

Next, using a contrast meter (EZ Contrast 160D from Eldim), the contrastratio of the reflection brightness of the display was measured. The dataof the contrast ratio in front of the display and the field of view(view angle) to give a contrast ratio of 3 are shown in Table 2.

Though the edges of the stretched film, of which the optical propertiesvary most significantly, were used for the optical compensating filmsherein and though the displays fabricated all had a relatively largepicture plane (diagonal length, 12 inches), good pictures were seen inthe entire region of the large picture plane.

5. Fabrication of HAN-Mode Reflection Liquid Crystal Displays:

A glass substrate with an ITO transparent electrode mounted thereon, anda glass substrate with a smooth reflective aluminium electrode mountedthereon were prepared. An orientation film of polyimide (SE-610 fromNissan Chemical) was formed on the electrode of the ITO transparentelectrode-having glass substrate, and rubbed. On the other hand, avertical orientation film (SE-1211 from Nissan Chemical) was formed onthe electrode of the reflective aluminium electrode-having glasssubstrate. The orientation film on the reflective aluminium electrodewas not rubbed. Via a 4.0 μm-spacer put therebetween, the two substrateswere stacked with their orientation films facing each other. A liquidcrystal (ZLI-1565 from Merck) was introduced into the space between thesubstrates to form a liquid crystal layer therebetween. The process gavea HAN-mode liquid crystal cell (diagonal length, 12 inches) having avalue Δnd of 519 nm.

Using an adhesive, the circularly polarizing plate that had beenfabricated in the above was stuck to the ITO transparentelectrode-having glass substrate on its side opposite to the side of theelectrode thereof. In addition, a light-diffusive film (Lumisty fromSumitomo Chemical) was stuck thereto.

A rectangular wave voltage of 55 Hz was applied to the thus-fabricated,reflection liquid crystal display. The display was visually checked at0.8 V for black expression and at 2.0 V for white expression. It wasconfirmed that both the white expression and the black expression wereneutral gray with no other color.

Next, using a contrast meter (EZ Contrast 160D from Eldim), the contrastratio of the reflection brightness of the display was measured. The dataof the contrast ratio in front of the display and the field of view(view angle) to give a contrast ratio of 3 are shown in Table 2.

Though the edges of the stretched film, of which the optical propertiesvary most significantly, were used for the optical compensating filmsherein and though the displays fabricated all had a relatively largepicture plane (diagonal length, 12 inches), good pictures were seen inthe entire region of the large picture plane.

6. Fabrication of VA-Mode Liquid Crystal Displays:

According to the process of Example 1 in JP-A 249223/2000, a transparentsupport was prepared for which, however, used was any of the opticalcompensating films 11 to 12 of the invention. According to the processof Example 3 therein, a polarizing plate was formed; and according tothe process of Example 5 therein, a VA-mode liquid crystal display wasconstructed. In stacking the optical compensating film and thepolarizing film in this, however, the two were so controlled that theabsorption axis of the polarizing film crosses the phase lag axis of theoptical compensating film at an angle of 45 degrees. The devices thusfabricated herein to have the optical compensating film of the inventionall had a broad field of view, concretely having a view angle of atleast 160 degrees in the vertical direction and a view angle of at least160 degrees in the horizontal direction. However, those having theoptical compensating film of Comparative Example 1 or 2 were not sogood, concretely having a view angle of 140 degrees in both the verticaldirection and the horizontal direction.

7. Fabrication of ECB-Mode Liquid Crystal Displays:

According to the process of Example 1 in JP-A 316378/1999, circularlypolarizing plates were fabricated in which, however, the opticalcompensating films 11 to 22 of the invention were used for the secondtransparent support. When the optical compensating film was stuck to thepolarizing film, they were so controlled that the absorption axis of thepolarizing film crosses the phase lag axis of the optical compensatingfilm at an angle of 45 degree. Using the circularly polarizing platesthus fabricated herein, ECB-mode liquid crystal displays wereconstructed according to the process of Example 6 in JP-A 316378/1999.The devices comprising the optical compensating film of the inventionall had a broad field of view, concretely having a view angle of atleast 120 degrees in the vertical direction and a view angle of at least115 degrees in the horizontal direction. However, the devices comprisingthe comparative, optical compensating film 23 were not so good,concretely having a view angle of not larger than 100 degrees in boththe vertical direction and the horizontal direction.

8. Fabrication of Organic EL Device-Having Displays, and Touch Panels:

In the touch panel having the constitution of FIG. 1 in JP-A127822/1993, used was any of the optical compensating films 11 to 23.Thus fabricated, the touch panels comprising the optical compensatingfilm of the invention all had a broad field of view, but thosecomprising the comparative, optical compensating film 23 did not.

In the organic EL device in Example 1 in JP-a 305729/1999, any of theoptical compensating films 21 to 22 of the invention or the comparative,optical compensating film 23 was used. Thus fabricated, the devicescomprising the optical compensating film of the invention had a broadfield of view, but those comprising he comparative, optical compensatingfilm did not.

INDUSTRIAL APPLICABILITY

According to the method of the invention, optical compensating filmshaving a large NZ factor and having good view angle characteristics(especially λ/4 plates having a phase difference of λ/4 in a broadwavelength range) can be stably produced on an industrial scale. Inparticular, in the method, the NZ factor of the optical compensatingfilms produced can be well controlled, without changing the retardationthereof, and therefore the method ensures industrial-scale stableproduction of optical compensating films having improved view anglecharacteristics.

In addition, image displays, especially reflection or semi-transmissionliquid crystal displays and organic electroluminescent device-havingimage displays that comprise the optical compensating film producedaccording to the method of the invention or comprise a polarizing platehaving the optical compensating film all have good view anglecharacteristics.

1. A method for producing an optical compensating film, which comprisesstretching a cellulose acetate film, the cellulose acetate film having awater content of 2.0 to 20.0% by weight, wherein the cellulose acetatefor the film has an acetyl value of from 57.0% to 62.5%.
 2. The methodfor producing an optical compensating film as claimed in claim 1,wherein the optical compensating film has a retardation value measuredat a wavelength of 550 nm (Re550) of 20 nm to 2000 nm: 20 nm≦Re550≦2000nm.
 3. The method for producing an optical compensating film as claimedin claim 1, wherein the optical compensating film has a distribution ofthe retardation value measured at a wavelength of 550 nm (Re550) of 10%or less in both a width direction and a longitudinal direction of thefilm.
 4. The method for producing an optical compensating film asclaimed in claim 1, wherein the optical compensating film has: theretardation value measured at a wavelength of 450 nm (Re450) of 60 to135 nm; and the retardation value measured at a wavelength of 590 nm(Re590) of 100 to 170 nm, and the stretched film satisfies thecondition: (Re590−Re450)≧2 nm.
 5. The method for producing an opticalcompensating film as claimed in claim 1, wherein the opticalcompensating film satisfies the conditions: 0.5<Re450/Re550<0.98; and1.01<Re650/Re550<1.35, in which Re450, Re550 and Re650 represent theretardation values measured at a wavelength of 450 nm, 550 nm and 650nm, respectively.
 6. The method for producing an optical compensatingfilm as claimed in claim 1, wherein the cellulose acetate film is dippedin water and/or exposed to water vapor to absorb water, before thestretch.
 7. The method for producing an optical compensating film asclaimed in claim 1, wherein no water film is substantially formed on thesurface of the cellulose acetate film when the cellulose acetate film isstretched.
 8. The method for producing an optical compensating film asclaimed in claim 1, wherein the water content of the cellulose acetatefilm just after having been stretched is 2.0 to 20.0% by weight.
 9. Themethod for producing an optical compensating film as claimed in claim 1,wherein, when L indicates the distance between the fixing members forfixing the cellulose acetate film when stretching and W indicates thewidth of the cellulose acetate film measured in the directionperpendicular to the fixing member-to-fixing member direction, theaspect ratio: L/W satisfies the condition: 0.1≦L/W≦2.
 10. The method forproducing an optical compensating film as claimed in claim 1, whichcomprises a step of stretching the cellulose acetate film between atleast two pairs of nip rolls by a difference in the rotation speedbetween the at least two pairs of nip rolls.
 11. The method forproducing an optical compensating film as claimed in claim 10, wherein,when W′ (cm) indicates the width of the cellulose acetate film and L′(cm) indicates the distance between the at least two pairs of nip rolls,the aspect ratio: L′/W′ satisfies the condition: 0.5≦L′/W′≦2.
 12. Themethod for producing an optical compensating film as claimed in claim 1,wherein the film is stretched in water.
 13. The method for producing anoptical compensating film as claimed in claim 1, wherein the film isstretched in air.
 14. The method for producing an optical compensatingfilm as claimed in claim 1, wherein the film is stretched in water vaporhaving a relative humidity of from 60% to 100%.
 15. The method forproducing an optical compensating film as claimed in claim 1, whereinthe film is stretched at a temperature of 50° C. to 150° C.
 16. Themethod for producing an optical compensating film as claimed in claim 1,wherein the film is stretched with a draw ratio of from 1.1 times to 2.0times.
 17. The method for producing an optical compensating film asclaimed in claim 1, wherein the stretching time is 1 second to 30seconds.
 18. The method for producing an optical compensating film asclaimed in claim 1, wherein the optical compensating film satisfies thecondition: 1≦(nx−nz)/(nx−ny)≦3, in which nx indicates the refractiveindex along the slow axis in plain of the optical compensating film, nyindicates the refractive index perpendicular to the slow axis in planeof the optical compensating film, and nz indicates the refractive indexof the film in the direction of the thickness thereof.
 19. The methodfor producing an optical compensating film as claimed in claim 1,wherein the optical compensating film has a haze value of 0 to 2%. 20.The method for producing an optical compensating film as claimed inclaim 1, wherein the cellulose acetate film contains an aromaticcompound having at least two aromatic rings in an amount of from 0.01 to20 parts by weight, based on 100 parts by weight of the film.
 21. Anoptical compensating film produced according to the method for producingan optical compensating film as described in claim
 1. 22. A polarizingplate, which is a laminate including: the optical compensating filmproduced according to the method for producing an optical compensatingfilm as described in claim 1; and at least one of a polarizing film anda polarizing plate.
 23. An image display comprising at least one of: theoptical compensating film produced according to the method for producingan optical compensating film as described in claim 1; and the polarizingplate, which is a laminate including: the optical compensating filmproduced according to the method for producing an optical compensatingfilm as described in claim 1; and at least one of a polarizing film anda polarizing plate.